Question

A hang glider flew to an altitude of 10000 feet. Fifteen minutes later, it's altitude was 7000 feet. What was the change in elevation per minute?

Answer 1

The speed is the change of distance over the change of time.
s = (d - d1)/(t - t1)
where the subscript 1 indicates as "initials."
The initial time starts at zero. So,
s = (7000 - 10000)/(15 - 0) = -200 feet (elevation) per minute
The value is negative because the hang glider flew downward.