What, roughly, is the percent uncertainty in the volume of a spherical beach ball whose radius is r = 2.86 plus or minus .09 m?

Question

I know I need to use the formula (4/3)*pi*r3 somewhere in this problem because of the details given, but I'm totally confused.

Answer 1

Add 2.86 + 0.09 and calculate volume.
Subtract 2.86 - 0.09 and calculate voluem. The uncertainty is the difference in the two volumes.

Answer 2

18.89%