I need help finding this missing angle

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.

Jonathan puts $400 in a bank account. each year the account earns 6% simple interest. how much interest will be earned in 5 years?

The length of the line segment ac is 8x-9 what is the value of x