Sav The monthly advertising revenue A and the monthly circulation x of a magazine are related approximately by the equation A-8x2-144 for x 12, where A is given in thousands of dollars and x is measured in thousands of copies sold. At what rate is the advertising revenue changing if the current circulation is x = 13 thousand copies and the circulation is growing at the rate of 5 thousand dA dA dx dt copies per month. (Hint: Use the chain rule: = (* dx dt The advertising revenue is changing at a rate of thousand dollars per month.