1. Calculate the volume of the bronze which is the difference between the outer sphere and the inner sphere.

Convert all measures into cm. If denote the outer radius and the radius of the inner sphere then the volume of the bronze is:

2. Since

3. Use the result from 1. to calculate the mass of the bronze.

4. If you are actually asked to find the weight of the bronze you have to multiply the result from 3. by

Spoiler: