Rainfall is measured in millimeters. The rain is collected in a vertical transparent tube with millimeter markings, and once the rain has stopped falling, one can check the height of the water in the tube.
In our problem, the tube unfortunately has a leak at height
L millimeters (mm). If the water level is above the leak then water drains from the tube at a rate of
K millimeters per hour (mm/h).
We want to figure out how much rain fell during a particular rainfall.
We assume that the tube is high enough that it does not overflow. We also assume that rain falls at an (unknown) uniform rate during a rainfall, and that water does not evaporate from the tube. The height of the leak itself is also negligible.