A rock is dropped from the top of a500-foot cliff. After 1second, the rock is traveling 44

feet per second. After 4 seconds, the rock is traveling 140 feet per second. Let y be the rate of descent and x be the number of seconds since the rock was dropped.

a. Write linear equation that relates time x to rate y.

b. Use this equation to determine the rate of travel of the rock 5 seconds after it was dropped.