Here's how I would do it.
(a) Radius of sphere
You get the radius of the sphere from the volume of the displaced water.
The formula for the volume
#color(blue)(bar(ul(|color(white)(a/a) V = 4/3πr^3color(white)(a/a)|)))" "#
We can rearrange this formula to get
(b) Density of metal block
You get the density
#color(blue)(bar(ul(|color(white)(a/a)ρ = m/Vcolor(white)(a/a)|)))" "#
(c) Density of wood
You apparently removed the metal sphere for this experiment.
The original volume was
The metal block had a volume of
When you submerged the wooden block,
∴The volume of the wooden block is
Assume that the mass of the wood is 7.5 g. Then