Question 386250
one plane at 520 feet is ascending at the rate of 40 ft per minute, while another plane at 3800 ft is 
descending at the rate of 120 ft per minute. 
How long will it take the 2 planes to be at the same altitude?
...

the difference between their heights = distance d
3800-520=3280 feet
..
their combined speed is 40+120=160 ft/minute =r
t=d/r
,,,
3280/160
=20.5 minute
{{{(highlight(t=20.5))}}}minutes