Problem 1

There is a water tank which is a cuboid with base area $x$, and height $h$. Standing in the tank are three identical metal columns, each a cylinder of height $h$, and base a circle of area $y$. The tank is then filled with a volume $v$ of water.

When one column is removed, the water level drops by $50$.

When a second column is removed, the water level drops by a further $30$.

Find how much further the water level drops when the last column is removed.