To find the surface area of the desing you need to find the are for all of the faces of the figure.
at the bottom we have a rectangular prism of sides 10, 10 and 2
sind the top, bottom and sides os this prism
total surface area at the bottom prism
for the prism at the top we just add the area from the sides because the top was already considered at the top of the previous prism
total surface are of the design is