Yh I think the missing number will be 6 because they are equivalent to 1:2
The answer would depend on where the numbers you gave us are on the pyramid. but here is the formula to find the surface area of a prism;
surface area= base x height + 2 x length x side + length x base
i will do the equation for you if you specify which numbers are the base, length, side, and height. or if you attach a photo.
