If a and b represent the height and base of the triangular face, and h represents the length of its hypotenuse, and w represents the width or thickness of the prism, the surface area (A) is
.. A = ab +w*(a +b+ h)
Of course the area of each triangle is (1/2)ab, but there are two of them, so their total area is ab.
Put in the numbers and do the arithmetic. If you have a lot of them all specified in this way, a spreadsheet can make short work of it.
A = 5*12 +4*(5 +12 +13) = 160 . . . square inches
