In the equation SA = 4πr^2h,

what happens to R if the height is tripled and the surface area stays the same.

SA, 4 and pi are all constants so you can ignore them.

* edit: had r and h reversed ...

1 = (3h) (r) ^2

1/3 = h (r) ^2

1/3 = (r) ^2

√ (1/3) = r

h and r are inversely related so tripling h will reduce r by 1/√ (3)