A hang glider flew an altitude of 10000 feet. 15 minutes later its altitude was 7000 feet. What was the average change in elevation per minute

So the change was 3000 feet.

And the amount of time was 15 minutes.

So by dividing 3000 by 15, you get about 200 feet per minute.

To check your answer when you do problems like this

Multiply the number of feet per minute, the answer of 200, by 15.

And it got 3000 so it's correct.