Please help me with this question

How to choose the sign of the radical in the denominator of the formula for the distance from a point to a line.

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.

Polynomial that can be factored as (3x-4)(3x+4)