We have two right triangles and three different rectangles.
The formula of an area of a right triangle:
l₁, l₂ - legs
We have l₁ = 20cm and l₂ = 21cm. Substitute:
The formula of an area of a rectangle:
l - length
w - width
We have:
rectangle #1: l = 22cm, w = 29cm
rectangle #2: l = 22cm, w = 21cm
rectangle #3: l = 22cm, w = 20cm
The total Surface Area of the triangular prism: