A hollow sphere with a wall made of titanium has a weight of $2\mathrm{.}5$ N and

dips into water with half of its volume.

a$)$ What is the diameter d of the sphere and the thickness x of the titanium

 

 wall? $$$$

 

 b$)$ What is the work W needed to pull the sphere out of the water?$\mathrm{}$$$