Surface area is the sum of area of all surfaces.
In the given diagram , we have two identical triangles , with height = 20 cm and base = 25 cm. Area of triangle = (1/2)*base * height.
So for the given triangle , area = 2*(1/2)*20*25 = 500 cm square .
We have a bottom rectangle whose area is 25*40 = 1000 cm square. A sideby rectangle, whose area is 35*40= 1400 cm square and a backwards rectangle, whose area is 20*40 = 800 cm square.
So the surface area = 500+1000+1400+800 =3700 cm square.
