 Once you have the equations for the sales of model A and model B, or brand A and brand B, I should say, we build the model, and you can build it in a number of configurations. This is just the way that seemed most logical to me. I set up sales that would contain my variables, the unit cost of A, 175 we started with, unit cost of B of 250, and then the price of A, I just said it 200, didn't matter, and the price of B, I said it 300. In the sales cell, we put our equations, and here's that first regression equation, the intercept minus the coefficient times the price of A, which is there in cell B8, plus the coefficient times the price of B, which is there in cell B9. Similarly, we have the other equation for the sales of B, our intercept plus the coefficient times the price of A at B8 minus the coefficient times the price of B9. So once we have those two sales figures, we can calculate revenue. Revenue is just equal to the number of units sold times the price per unit. And cost, we're going to get the total cost, and that's based on the number of units sold there in C8, multiplied times the cost of A there in B4, and that gives us cost. If you build your model this way, then we can go back and vary these prices, I'm sorry, the cost of A, and we can vary the prices of A and B, and that'll change our model. Profit of course is just equal to revenue minus cost, and then I sum those down to get the total revenue, total cost, and total profit, which is the difference of revenue and cost. Okay, we've got our model. Now, first of all, we will use the goal seek trying to achieve a certain revenue. I forget what the problem was, we'll just make one up. We go to data, what if, goal seek. And our first is asking us to pick the cell that we want to achieve our goal, and I'm going to say revenue in D10, and I want it to be a value of $78,000, and I'm going to do it by changing a cell. We're going to change the price, but we can only change one cell at a time. I'm just going to click the price of A. Now, if you remember, because these are dependent on one another, when I change the price of A, I'm impacting the sales of A and the sales of B. So we can optimize or hit our goal just by changing that one cell. Click on OK, and just a few seconds, it's calculated to get our revenue of $78,000. We needed to set a price of $152.47 on A and a price of $300 on B, and we've achieved our revenue. Okay, let's now do Solver. We're going to click on data, Solver, and bring up our dialog box. Our objective this time, clicking that set objective, is going to be profit, and we want to maximize profit, and we're going to be changing cells. In this case, we're going to be changing both the price of A and the price of B, and I've got a constraint already in here, like the one I was messing around with it, and it says I want C8, which is the number of units of Model A, Brand A, Sol, to be less than or equal to 125, and let's just for the heck of it, add a second constraint, and in this case, I'm just sticking off the top of my head here, I want to set my total revenue to be greater than or equal 125, I'm sorry, 125,000, and that may work. I add that constraint, now I've got my Solver set up, I've got two constraints, and we want to maximize the profit, we're going to leave these default values there, and click on Solve, whoops, so I've given it constraints that it couldn't do both of those, so that tells me that I gave it an unrealistic situation, so let's go back, and I'm going to go back to Solver, and I'm thinking it's that one there, I want to change it, and let's try dropping that down to 95,000, okay, now let's see if it'll solve, okay, that time it did give us a solution, we've maximized profit, keeping the total sales of Model A below 125, we may have had a constraint from our manufacturer, and we've achieved our revenue of at least 95,000, 95,007 cents, so that's really how you use Solver, hope that helps.