1. The problem statement, all variables and given/known data Through market research, a computer manufacturer found that x thousand units of its new laptop will sell at a price of 2000 - 5x dollars per unit. The cost, C, in dollars of producing this many units is C(x) = 15 000 000 +1 800 000x + 75x^2. Determine the level of sales that will maximize profit. 2. Relevant equations Profit = Revenue - Cost 3. The attempt at a solution I said Revenue = 2000 - 5x and Cost = 15 000 000 +1 800 000x + 75x^2 Using the formula Profit = Revenue - Cost I subtracted them from each other and got: Profit = -14998000 - 1800005x - 75x^2 Then I found the derivative which came out to be: P'(x) = -1800005 - 150x Then I set it equal to zero and solved for x: 0 = -1800005 - 150x 1800005 = -150x x = -12000.03 but the answer in the back of the book is 19 704 units. Can anyone explain what I did wrong?