Hello, Athena,
The equation y=-2x2+100x+60 is a parabola. What you want is the highest point on that parabola, where y (the profit) is highest. x (the price of one designer bag) will be the point where the curve stops going up and starts heading down. The slope of the line at this point is zero.
We can find the optimum price in one of two ways:
A. Graph it. Then find the value of x where the parabola peaks:
B. Obtain the first derivative and set it to 0, the slope at the highest point:
y=-2x2+100x+60
dy/dx = -4x +100
0 = -4x + 100
x = 25
$25 is the price that will bring the highest income.
The total revenue would be -2(25)2 + 100(25) +60 = $1,310
Bob
Bob

Robert S.
01/28/21
Athena F.
thanks01/28/21