Two hoses together fill a pool in 2 h. If

only hose A is used, the pool fills in 3 h.
How long would it take to fill the pool if
only hose B were used?

3 answers

T = 2 h.
Ta = 3 h.
Tb = ?

T = Ta*Tb/(Ta+Tb) = 2.
3*Tb/(3+Tb) = 2.
Tb = ?.
rate of hose B = 1/b
rate of hose A = 1/3
combined rate = 1/b + 1/3 = (b+3)/(3b)

so 1/( (b+3)/(3b)) = 2
3b/(b+3) = 2
3b = 2b + 6
b = 6

Just noticed this looks just like Henry's
Yes, it is I, your humble servant(LOL).