.The demand function
where p = price in dollars and x = sales level in hundreds, is pictured below.
The area of the grey rectangle in the picture has area = sales level times price = revenue generated by sales.
The area of the shaded portion under the curve above the rectangle represents the consumers' surplus.
for a sales level of 900 ...
First find the price ... evaluate p(900)
then revenue from sales ... 900[p(900)]
consumers' surplus ... - 900[p(900)]
Note: The consumers' surplus formula involves p(x) and hence x values must be in hundreds. The output of the consumers' surplus integral is in hundreds of dollars though, so be careful with your units!