Question 22530
First set up the equation of proportionality: Let F = flow in gallons and T = time in hours.

{{{F = kT}}} where k is the constant of proportionality.  Solve for k.
{{{k = F/T}}}  Substitute F = 350 gallons and T = 20 mins = 1/3 hour.
{{{k = 350/(1/3)}}}
{{{k = 350(3)}}}
{{{k = 1050}}}

Now you can solve the problem:
{{{T = F/k}}} Substitute F = 3000 gallons and k = 1050
{{{T = 3000/1050}}}
{{{T = 2.857}}}hrs
T = 2 hrs. 51 mins. 25.2 secs.