Then the influent is110, and the effluent is 1/20.

The remaining110-1/20.

Also1-(110-1/20)

Full 10 hour

So1-(110-1/20) should be10 * [1-(110-)

10*[ 1-( 1/ 10- 1/20)]= 10* 19/20=9.5

So it takes 9.5 hours.