One Way to Determine the Speed of the Current of a River

Multiple Choice

One way to determine the speed of the current of a river is to measure how long it takes a leaf to pass under a bridge. For example, let's say it takes a leaf 7 seconds to pass under a bridge that is 30 feet wide. What is the speed of the current in feet per hour? Round to the nearest integer. ​

A) 12,857 feet per hour
B) 2571 feet per hour
C) 2 feet per hour
D) 514 feet per hour
E) 15,429 feet per hour