What is K squared minus 11

Suppose that the price p (in dollars) and the weekly sales x (in thousands of units) of a certain commodity satisfy the demand equation 4p cubedplusx squaredequals38 comma 400. determine the rate at which sales are changing at a time when xequals80, pequals20, and the price is falling at the rate of $.20 per week.

Can someone me i’m confused. will give brainliest and a whole bunch of points

What number should be added to the expression x^2+3x+ in order to create a perfect square trinomial? 3/2 3 9/4 9