A boat has a speed of 15 mph in calm water. It takes the boat 3 hours to travel upstream but only 2 hours to travel the same distance downstream. Which equation can be used to find c , the speed of the current in miles per hour?

The boat’s upstream speed is 15 − c mph, so in 3 hours it travels 3(15 − c) miles. Its downstream speed is 15 + c mph, so in 2 hours it travels 2(15 + c) miles. Since the distances are the same, set these expressions equal: 3(15 − c) = 2(15 + c), which is choice D.

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