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**HallsofIvy** The balloon is moving **horizontally**, keeping a constant height. t **hours** after crossing the intersection, the horizontal distance from the intersection is 15t **miles** and the balloons vertical distance is 100 **feet**. The straight line distance from the intersection to the balloon is along the hypotenuse of a right triangle having the horizontal and vertical distances as legs. Yes, you need to use the Pythagorean theorem. Since the problem asks for the distance in **feet** in t seconds, you will need to convert 15 "miles per hour" to "feet per second".

(There are 5280 feet in a mile and 3600 seconds in an hour.)