 So one of the important things we have to be able to do is to solve an equation for a specific variable. So I suppose we have the equation A equals one-half BH. And we want to solve this for H. So there are three important things to keep in mind when solving equations. First, to solve an equation for a variable, we want to rewrite the equation in the form variable equals stuff that doesn't include the variable. Second, the type of expression or equation is determined by the last operation performed. And third, you have to undo the last thing first. So if we take a look at the equation A equals one-half BH, we see that this is a product. And so we begin by dividing. Now remember we need to be a little bit careful with division. We should avoid dividing by an expression containing the variable we want to solve for. So if we think about this equation as the product one-half times B times H, we're multiplying H by one-half B. And so that means we'll divide by one-half B. And so now we have H equal to a whole bunch of things that don't include the variable H we've solved for the variable. Although the form isn't particularly nice. Well, we don't have to do it. It's nice not to have a fraction in the denominator. So we can simplify our expression. Remember if we multiply numerator and denominator by the same thing, we get an equivalent fraction. And if we multiply a fraction by its denominator, that will clear out the fraction. So here this fraction one-half in the denominator, if we multiply it by two, we'll get rid of the fraction. We also have to multiply the numerator by two to keep the same expression. And that gives us a simplified form of our answer. How about the equation P equals 2L plus 2W solved for W? So again to solve an equation for a variable, we want to rewrite the equation in the form variable equals stuff that doesn't include the variable. The type of expression or equation is determined by the last operation performed. And you have to undo the last thing first. So our expression 2L plus 2W has a multiplication, 2L, 2W, and an addition. We have to do the multiplication first, which means the addition is done last. And so the expression is a sum. So we should begin by subtracting. Since we want to solve for W, we want to get W all by itself. We'll subtract 2L. So again we're trying to solve for W. We had an addition. We've taken care of that. We also have a multiplication. So now we want to divide by two. And now we have our equation in the form W equals stuff that doesn't include W. We've solved for W. So let's solve this for R to solve an equation for a variable. We want to rewrite it in the form variable equals stuff that doesn't include the variable. The type of expression or equation is determined by the last operation performed. And you have to undo the last thing first. So what we have, we have a bunch of divides. We have a sum. Order of operation says the divides have to be taken care of first and then the sum. So the last thing done is a sum. And so the expression is a sum. And since we're trying to solve for R, we'll subtract 1 over Q. So at this point it's helpful to think about all the stuff that doesn't involve R as things we can take care of first. And that means all this stuff over on the left hand side, we don't really care what the operations are. The only thing that matters are the operations that are actually being done with R. And so over here on the right hand side, we have 1 over R. Well that's really 1 divided by R. The expression involving R is a quotient. And since we're dividing by R, to undo this we should multiply by R. And over on the right hand side, our common factors of R drop out. And over on the left hand side, we do nothing because factored form is best and we have a product. And so the expression involving R is a product and so we should divide. And again, typically we want to avoid dividing by an expression containing the variable we want to solve for. So we want to divide by this entire expression 1 over T minus 1 over Q. And that gives us our final answer.