First, find the area of the base. Using the formula for the area of a trap.,
L1 + L2
A = -------------- W (where L1=11, L2=18 and W=7)
2
11 + 18
Here: A = ------------- * 7 = 101.5 cm^2.
2
Multiply this result by 2, since the prism has both a top and a bottom surface.
Thus: 2(101.5 cm^2) = 203 cm^2.
Now we need to find the surface areas of the vertical sides. In all four cases the height is 8 cm. One such area is 7*8 cm^2, followed by 11*8 cm^2, followed by 10*8 and 18*8 cm^2. Result: (8 cm)(7 cm + 11 cm + 10 cm + 18 cm) = 8(46) cm^2 = 368 cm^2.
Finally, add together these two results (side areas and top and bottom areas): 203 cm^2 + 368 cm^2 = 571 cm^2
