The bases of the prism are the triangular faces.
One side is marked 3 units. The vertical sides to the left of the triangles are 4 units. In a right triangle, if the legs measure 3 and 4, the hypotenuse measures 5.
The three sides of the triangular base measure 3, 4, and 5.
Perimeter = sum of the lengths of the sides
Perimeter = 3 + 4 + 5 = 12
Answer: 12 units