Economics—Consumer Spending: Social networking and Internet commerce have contributed to t...

Economics—Consumer Spending: Social networking and Internet commerce have contributed to the amount of spending on video and audio products during the past two decades. The amount spent on audio and video products in the United States from 1990 to 2010 can be modeled by

where x represents the number of years since 1990 and f(x) represents the amount spent on audio and video products, measured in billions of dollars. (Source: U.S. Bureau of Economic Analysis).

(a) Determine f′(x).

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(b) Use the results of part (a) to determine the rate at which spending on video and audio products was increasing in 2008.