B alone can empty the pool in 5.744 hours, if A alone can empty the pool in 4.75 hours and it takes 2.6 hours when both drains are turned on.
Explanation:
The given is,
A alone can empty the pool in 4.75 hours.
It takes 2.6 hours when both drains are turned on.
Step:1
One hour work drains A and B =
One hour work of drain A + One hour work of Drain B.........(1)
One hour work of Drain A =

One hour of ( A + B ) =

Equation (1) becomes,
One hour work of B = One hour work of ( A + B )
- One hour work of A
Substitute the values,
One hour work of B =

=

=

=

One hour work of B =

B alone can empty the pool in 5.744 hours
Result:
B alone can empty the pool in 5.744 hours, if A alone can empty the pool in 4.75 hours and it takes 2.6 hours when both drains are turned on.