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put this solution on YOUR website!The elvator went at 4m/s at a distacne of x
The elvator reutrned at 5m/s at a distance of x
Total time in SECONDS. because its meters per second. (4*2+1)/2=4.5*60=270s
270s-90s=180s

4*5 =20
5*4=20
Hence the common multiple is 20

Simplfy the expression.
5x+4x=3600
9x=3600
x=400
Hence the tower is 400m tall.
Paul.