A parachutist's elevation changes by -143 ft in 13 seconds. What is the change in the parachutist's elevation each second?

He actually falls an AVERAGE of 11 feet per second.

If he was in freefall then he would be accelerating at approx 32 feet per second so he would be going much faster at the end than at the beginning.

Divide 143 by 13. That gets you 11. That means that he falls 11 feet per second.