To find the Surface Area of a Triangular based prism you need to use the following formula: SA= bXh÷2 X H (of the prism)
In the question you have shown, the height is 8in, the base is 7in, and the height of the prism is 16in
so SA= 7X8÷2X16
= 448in^2
Therefore the Surface Area is 448in^2. Hope that helped!!