Let V be the volume of pool.
`{:("Taps:",I,II,III),("No .of hours:",x+5,x,x-4):}`
Parts of the pool filled by first, second and third pipe in one hour are respectively
`(V)/(x+5),(V)/(x),(V)/(x-4)`
It is given that, `(V)/(x+5)+(V)/(x)=(V)/(x-4)`
`implies(1)/(5+x)+(1)/(x)=(1)/(x-4)`
`implies(x+x+5)/(x(x+5))=(1)/(x-4)`
`implies(2x+5)(x-4)=x(x+5)`
`implies2x^(2)-3x-20=x^(2)+5x`
`impliesx^(2)-8x-20=0`
`implies(x-10)(x+2)=0`
`because"either "x=10orx=-2`
But, hours cannot be in negative.
So, we reject x=-2
`because` x=10
Hence, the first, second and third pipe fill the pool in `10+5 ,10,10-4 i.e.,15,10` and 6 hrs respectively.