The Monthly Sales of Sunny Electronics' New Stereo System Is $S ( x ) = 30 x - x ^ { 2 }$

Multiple Choice

The monthly sales of Sunny Electronics' new stereo system is given by $S ( x ) = 30 x - x ^ { 2 }$ hundred units per month, x months after its introduction. The price Sunny charges is $p ( x ) = 1,000 - x ^ { 2 }$ dollars per stereo system, x months after its introduction. The revenue Sunny earns then must be $R ( x ) = 100 p ( x ) S ( x )$ . Find the rate of change of revenue 6 months after introduction. Round your answer to the nearest dollar.

A) $437,700 per month
B) $43,770 per month
C) $1,562,400 per month
D) -$391,800 per month
E) -$322,700 per month