336First let's calculate the surface area of the front face of the bigger prism:
This surface area of 12*7=84, is the same area of the back face and left and right faces. Then there is 4 faces with this 84 surface area, being the total 84*4=336
Now, the base of the bigger prism is algo a surface area, wich is a square of length side 7, then the surface area of the base is 49:
Now, the top of the figure without the smaller blue prism would be another square with 7 as the length of the side, being 7*7=49 the top surface. How ever, the top face has a smaller prism on, which is covering a part of this 49 cm^2. The part covered is 2cm*7cm, the area of the bottom face of the blue prism. Hence, the top surfaces from the bigger prism is 49-2*7=35.
Finally, the surface area from the blue small prism is the top face, with an area of 7*2=14, the right and left faces with the same 14 of area (then there is 3 faces with 14 of surface area), and the front and back faces which are squares with an area of 2*2=4 each one (then there is two faces with 4 as surface area).
The total surface area is: