Here, Just need to apply the formula of "Volume of Cylinder"
We know, Volume of a Cylinder = πr²h
In 1st condition (when dispenser is full),
5652 = 3.14 * 7.5² * h₁
5652 = 176.625 * h₁
h₁ = 5652/176.625
h₁ = 32 cm
Now, In 2nd Condition (when dispenser is not fulled),
4239 = 3.14 * 7.5² * h₂
4239 = 176.625 * h₂
h₂ = 4239 / 176.625
h₂ = 24 cm
Now, Difference = h₁ - h₂
Δh = 32 - 24 = 8 cm
In short, Your Final Answer would be 8 cm
Hope this helps!