Answer:
1) When r = 2, M = 20.
2) When M = 540, r = 6.
Explanation:
M is a directly proportional to r cubed
This means that the equation for M has the following format:

In which a is a multiplier.
When r=4 M=160.
We use this to find a. So





So

1) work out the value of M when r=2

When r = 2, M = 20.
2) work out the value of r when M=540




![r = \sqrt[3]{216}](https://img.qammunity.org/2022/formulas/mathematics/college/6ho1xh5dxbvu2fezad20mqofrjgouxlb8o.png)

When M = 540, r = 6.