A hollow sphere if inner radius 80 cm and outer radius 90

Question

Compute the given parts of following problem:

Problem: A hollow sphere if inner radius 8.0 cm and outer radius 9.0 cm floats half submerged in a liquid of density 800 kg/m³.

Part A: What is the mass of the sphere?

Part B: Calculate the density of the material of which the sphere is made

Part C: If the density of the liquid is increased to a 1000 kg/m³, what will happen - explain in words or equations.

I need tutor help to solve the above problem.