**A distillate flows into an empty 64-gallon drum at spout A and out of the drum at spout B. If the rate of flow through A is 2 gallons per hour, how many gallons per hour must flow out at spout B so that the drum is full in exactly 96 hours?**

A) 3/8

B) 1/2

C) 2/3

D) 4/3

E) 8/3

Answer: **D**

I solved this by saying at its current rate, it will take 32 hours to fill this drum. But I want it to take 96 hours, so I’d like my speed to be 1/3 as fast.

So I want Unit B to “take away” 2/3 of the amount each time Unit A does one unit of work. 2-(2/3) = 4/3.

I got the correct answer but I am thinking algebra might be a better way to go about these questions. I watched Greg’s explanation on this but don’t understand how to approach doing algebra with two different rates. Can anyone clarify this process for me? Thanks