Call me ranch cuz i be dressing

The surface area (sa) of a cube with a as the length of each of its sides is given by the formula . if the surface area is known, how can you rewrite the formula to find its side?

Can you me find the missing length. i attached an image.

I’m on question 7 it says a covered water tank is in the shape of a cylinder the tank has a 28 inch diameter and a height of 66 inches to the nearest square inch what is the surface area of the water tank