Question 133199
The first pump can fill 1/4 tank per hour. The second pump can fill 1/3 tank per hour.

The two working together can fill:
{{{t/4 + t/3}}} per hour
{{{3t/12 + 4t/12}}}
{{{7t/12}}} per hour

In order to fill the tank, you will need to run the two pumps for {{{12/7}}} hours