A rock is dropped from the top of a​ 500-foot cliff. After 1​ second, 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 a linear equation that relates time x to rate y.​ Hint: Use the ordered pairs ​(1,​44) and ​(4,140​).
b. Use this equation to determine the rate of travel of the rock 5 seconds after it was dropped.