please help me with this question. I just can't figure it out.

A cylindrical jar of radius 6cm contains water. How many iron solid spheres each of radius 1.5cm are required to immerse into the jar to raise the level of water by 2cm?

Volume of water rise = π(6^2)(2) = 72π

volume of 1 sphere = (4/3)π(1.5)^3 = 4.5π

number of spheres that caused the rise
= 72π/4.5π
= 72/4.5
= 16