Question 404877
This is a rate problem.
Add the rates to get the resulting rate.
Filling the sink in a (+) rate
Emptying the sink is a (-) rate 
The best way to understand it is
to express solution in words.
(1 sink filled)/(minutes to fill sink) - (1 sink drained)/(minutes to drain sink) = (1 sink filled)/(minutes to fill sink w/drain and faucet open)
{{{1/3 - 1/4 = 1/x}}}
Multiply both sides by {{{12x}}}
{{{4x - 3x = 12}}}
{{{x = 12}}}
It takes 12 min for the sink to overflow with faucet
and drain open