Answer: 24hours
Explanation:
We list the conditions as A and B
a. If inlet pipe #1 will fill the pool in 8 hours, the the portion of the pool that will be filled in one hour by inlet pipe 1 = 1/8.
b. If inlet pipe #1 and #2 will fill the pool in 6 hours, then the portion of the pool that inlets pipe #1 and #2 combined will fill in one hour = 1/6.
Now to get the portion of the pool that will be filled in one hour if only inlet #2 is running becomes:
condition b - condition a
= 1/6 - 1/8
= 2/48
= 1/24.
Since 1/24 is the portion of the pool that will be filled in one hour, then it will take 24hours for inlet #2 alone to fill the entire pool.