The easy part: The volume of a sphere of radius r is given by [tex]\frac{4}{3}\pi r^3[/itex]. So the 100 mm sphere will have volume . The 20 micro millimeter coating will add .02 millimeters to the radius and a 100.002 mm sphere will have volume [tex]\frac{4}{3}\pi (100.02)^3[/quote].

The difference in the two volumes, , is the volume of chromium needed.

Now, the rest of the problem depends upon how fast that chromium can be deposited depends upon information I don't have but I suspect you do. In particular, I have no idea how you would use the equation you give, w= itA/2F, because I have no idea what those letters represent. You should have learned that when you learned the formula.