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What are the soultion(s) to the quadratic equation 40- x^2=0

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.

Find the slope and the y-intercept if there's one and the equation of the line given these two points( 3, 2) and( 3, -4)