Find the geometric mean of 4 and 12

Can someone check if i did this right since i really want to make sure it’s correct. if you do you so much

The ratio of the measures of the three angles in a triangle is 2: 9: 4. find the measures of the angels

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