Question 98063
flow*time=volume f*t=v f=v/t
let v=100 gallons actually it can be any number you choose and the answer will be the same.
100/30=10/3
100/45=20/9
10/3-20/9=90/27-60/27=30/27=10/9 (10 gal leaves the tank every 9 minutes) So in 90 min the tank will be empty.
if you like formulas you can do a proportion:
10/9=100/t
10x/9=100
t=100*9/10=90 min
Ed