math
posted by Sena on .
one elevator leaves first floor of a building at 9:00 a.m. It takes 5 seconds to travel between floors, stays 10 seconds at each floor and stops at each floor on its way to the top. Another elevator leaves the 12th (top) floor at 9:00 a.m. ; it takes 5 seconds to travel between floors, stays 15 seconds at each floor and stops at each floor on its way to the bottom. On what floor will both elevators be available at the same time?

time floor
0 1
05 12
515 2
1520 23
2030 3
3035 34
3545 4
4550 45
5060 5
6065 56
6575 6
7580 67
8090 7
9095 78
0 12
05 1112
520 11
2025 1011
2540 10
4045 910
4560 9
6065 89
6580 8
8085 78
85100 7
for t 8590 both are on floor 7