Jack starts at the summit of Mt Mickinley elevation 20320 an

Jack starts at the summit of Mt. Mickinley (elevation 20,320) and travels down the mountain at a rate of 4 feet per second. Jill starts at the bottom at the same time and travels up the mountain at a rate of 1 foot per second. At what elevation, in feet, will they meet?

Solution

4x+1x=20,320
5x=20,320
x=20,320/5
x=4,064 sec. after they start they will meet.
1*4,064=4,064 feet is the meeting altitude.
Proof:
4*4064=16,256 feet below the peak.
16,256+4,064=20,320
20,320=20,320