Question 167811
You have found the turning point which will give the maximum area correctly.

I would suspect that your calculator is not set to show such a wide range of x and y. Make sure that it will display x up to 200 and the y value up to 10000. The graph should then display.
{{{ graph( 300, 200, 0, 200, 0, 10000, x-2, -x^2+200x)}}}