Given:
Consider the triangular part in the given figure.
To find the third side of right triangle. Use pythagorean theorem,

The missing side of triangle is 5 cm.
Now to find the surface area of triangular prism.
Note that the height of the right triangle is 4 cm and base is 3 cm.

First calculate the area of each side,

So, the surface area is,

Answer: surface area is 84 square cm.