Answer:
The maximum revenue is 16000 dollars (at p = 40)
Explanation:
One way to find the maximum value is derivatives. The first derivative is used to find where the slope of function will be zero.
Given function is:

Taking derivative wrt p

Now putting R'(p) = 0

As p is is positive and the second derivative is -20, the function will have maximum value at p = 40
Putting p=40 in function

The maximum revenue is 16000 dollars (at p = 40)