Which equation represents a line which is parallel to the x-axis?

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.

Anyone? 15m is what percent of 60m; 3m; 30m; 1.5 km?

Ftara spends $219 a month for her car payment and she makes $3,200 a month, what percent of her monthly income is spent on her car payment?