We are given the formula for volume V:
V = 3.14 r^2 h
where r is radius and h is height
The standard height and radius is both 20 cm each, therefore we can write it as:
V = 3.14 (20)^2 (20)
It is stated that the radius can be modified, for every 1 cm change in tanks radius, the height must increase by 5 cm, therefore:
V = 3.14 (20 – x)^2 (20 + 5x)
or in general form:
V = 3.14 (r – x)^2 (h + 5x)