 So we're going to look at now function notation in modeling. So let's say that we want to write an equation to represent population in Hawaii. And it's since 2000, and the population is in millions. So we would start out with P of t. We have to name the function. Since we're talking about population, then I'm going to call it P of t because we're talking about time as part of our stipulations here since 2000. So this will be P of t is a population of Hawaii in millions, and that t is going to represent the years since 2000. So here's the function that they gave us. P of t is equal to 0.013 t plus 1.21. If we're given P of 10, we have to determine, well, what is the 10 so that when we finish we know what we found? Well, the 10 is inside the parentheses, and if you go back to our function notation, it was t is inside the parentheses. So this 10 must be years since 2000, or we could say it's going to be in 2010. All right, so to find P of 10 then, remember that wherever you see a t in the function, we're going to replace it with the 10. So we put 0.013 times 10 plus 1.21. Again, remember what's inside the parentheses here replaces the variable, so that's why we have a 10 here. When we multiply here, we get 0.13 plus 1.21, and if we add 0.13 plus 1.21, we get 1.34, which means million people in 2000, in Hawaii we should say, in 2010. Okay, now, what if we have P of t is equal to 4? Remember, this is like our y is equal to 4. So when it says P of t is equal to 0.013 t plus 1.21, P of t is equal to 4, so this is P of t, so we put 4 on that side, where we would normally think of y, equal to 0.013 t plus 1.21. If we subtract 1.21 from 4, we get 2.79 equal to our 0.013 t, and if we divide by 0.013, we find out that t is 214.6, or we'll say it's approximately 215 years after 2000, or 2215, the population will be 4 million.