one plane at 520 feet is ascending at the rate of 40 ft per minute, while another plane at 3800 ft is

Question

descending at the rate of 120 ft per minute.
How long will it take the 2 planes to be at the same altitude?

Answer 1

Equate their altitudes in feet and solve for t (in minutes):

520+40t = 3800 - 120t