At 6 A. a snowplow, traveling at a constant speed, begins to clear a highway leading out of town. At 8 A.

At 6 A.M. a snowplow, traveling at a constant speed, begins to clear a highway leading out of town. At 8 A.M. an automobile begins traveling the highway at a speed of 45 mi/hr and reaches the plow 15 minutes later. Find the speed of the snowplow.