Question 704592
Pump A rate = 1/4 tank per hour
Pump B rate = 1/6 tank per hour
Both pumps together rate = 1/4 + 1/6 tank per hour

Time pump A alone = 1 hour
Time pumpts together = t-1 hour
t, unknown time in hours.


Sum of jobs = The Whole Job.
(1/4)*1 amount of the job for A while worked alone
(1/4+1/6)*(t-1) amount of job for both pumps together


{{{(1/4)*1+(1/4+1/6)*(t-1)=1}}}, the whole tank job.
.
.
{{{t=14/5=2&4/5}}} hours