Question 962365
Let x= amount of time for pool to fill
with both pipes open the pool fills at the rate of 1/x pool per  hour
Hose fills at rate of 1/12 pool per hour
Drainage  pipe empties at rate of 1/18 pool per hour
sooo
1/12 - 1/18= 1/x multiply each term by 36x to get rid of fractions
3x-2x=36
x=36 hours ---
CK
In 36 hours fill pipe fills (1/12)*36= 3 pools
In 36 hours drain pipe  drains(1/18)*36=2 pools
3-2=1 full pool:)

hope this helps--- ptaylor