Answer:
I. 336 ft²
Explanation:
We have
two right triangle with legs 6ft and 8ft
one rectangle 8ft × 12ft
one rectangle 6ft × 12ft
one rectangle 10ft × 12ft
The formula of an area of a right triangle:

a,b - legs
Substitute:

The formula of an area of a rectangle:

l,w - length, width (dimensions of rectangle)
Substitute:

The Surface Area:
