Answer:
The tank is 10cm high
Explanation:
Given
-- length
-- width
--- water lever

Required
The height of the tank
Let y represents the remaining fraction before water is added.
So:

Make y the subject


Solve


Represent the volume of the tank with v
So:

Make v the subject

Substitute:



Represent the height of the tank with h;
So, the volume of the tank is:

Make h the subject

Substitute values for v, l and w

Convert 30L to cm^3


