Answer:
time require is 23.33 hours
Step-by-step explanation:
given data
time t1 = 7 hours
time t2 = 10 hours
to find out
how long it take to fill vat if both pipe left open
solution
we consider here vat volume is v
so speed = volume / time .................1
inlet speed = v / 7 .................2
outlet speed = v / 10 ..................3
so from equation 2 and 3
net speed is = v / 7 - v / 10
net speed = 3 /70 × v
so here time is
time = v / net speed
time =

time = 70 / 3 = 23.33
so time require is 23.33 hours