The Monthly Sales of Sunny Electronics' New Stereo System Is $S ( x ) = 10 x - x ^ { 2 }$

Short Answer

The monthly sales of Sunny Electronics' new stereo system is given by $S ( x ) = 10 x - x ^ { 2 }$ hundred units per month, x months after its introduction. The price Sunny charges is $p ( x ) = 1,200 - x ^ { 2 }$ 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 10 months after introduction.
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Please enter your answer in dollars/month without the units.