https://www.gregmat.com/problems/quant?problem=a-man-is-filling-at-a-constant-rate
How do we know that it should be b-225 and not 225-b?
The exit rate has to be bigger so that overall, the water will be drained out in 12hrs.
In other words, the water that will be filled by the filling rate needs to be taken out by the exit rate while taking out the 1350 volume simultaneously.