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Question:

Monthly demand for gasoline at a particular location, as a function of the price of gasoline and the price of bus travel, is given (in hundreds of gallons) as $4286_w211_h19.png$. The slope of the demand curve for gasoline is closest to:

A -0.07.
Explaination

The demand curve (price as a function of ${Q_D}$) is found by inverting the demand function:
$7086_w218_h37.png$
The slope of this function (for any positive value of ${P_{bus}}$) s -1/15, or -0.0667.