The formula to find the surface area of a right triangular prism is SA = bh + (s1 + s2 + s3)H. bh is the base times the height of the right triangle, and notice we do not do 1/2 base times height because there are 2 right triangles, one in the front and the other at the other end of the prism. This is 4*3 = 12 units squared. Next, we calculate the sum of the length of the sides of the 3 rectangles by the height of the prisms. We see that the height of this prism is 11 units, and there are sides of length 3, 4, and 5 units. So if we plug it into the formula, we have (3 + 4 + 5) * 11 = 12 * 11 = 132 units. Add that to the area of the triangles we calculated earlier and you have a total surface area of 144 units squared.
We can also label the length (l), width (w), and height (h) of the prism and use the formula, SA=2lw+2lh+2hw, to find the surface area. Hope this helps!
