Differentiate your equation, sub in what you are given and find dx/dt.
Suppose that the price p (in dollars) and the weekly sales x (in thousands of units) of a certain commodity satisfy the demand equation 2p^3 + x^2 = 4500.
Determine the rate at which sales are changing at a time when x = 50, p = 10, and the price is falling at the rate of $0.50 per week. (Thanks in advance!)