# Frustums of sphere

**Geometry**Level pending

You are given a frustum of a sphere with height of 4 cm, upper base radius of 2 cm, and lower base radius of 3 cm.. If the square of the radius of the sphere can be expressed in the form of \(\frac ab\) for coprime positive integers \(a\) and \(b\), find the value of \(a-b\).