In a triangular prism, the two triangular faces will have equal side and height measures. You were given the height of one of these triangles--8, which means you know the height of the other right triangle.
Formula for area of a right triangle is:
A = (1/2)bh
h= 8
For the base: you were given 12 for the length of the total triangle; right angle bisects that, which means it divides into two--base = 6. You could also use the Pythagorean Theorem since you were given a hypotenuse of 10--10^2 = 8 ^2 + b^2; b^2= 36, b = 6
A = (1/2)(8)(6) = 24
But that's only one right triangle out of four--the two triangle faces are composed of two right triangles each. So multiply that area by 4 to get the total area of your triangles:
4A = 4(24) = 96
Now, the rectangles are easier to work with:
A=lw; l = 15.5, w = 10
A = 155
But you have two of these, so multiply:
2A = 2(155) = 310
Now, we have one more face to deal with: the base, also a rectangle, but with different width:
A=lw
l = 15.5, w = 12
A= (15.5*12) = 186
Add up everything in bold:
SA = 96 + 310 + 186 = 592
I hope this helps.