Check the picture below.
part A
since the base of the triangular base is 16, and the altitude "h" splits the base in two equal halves, half that is just 8, so we're looking at a right triangle with a hypotenuse of 17 and a side of 8, thus

part B
well, the prism is simply two triangles and 3 rectangles, le's simply add their areas.
![\stackrel{two~triangles}{2\left[ \cfrac{1}{2}(\stackrel{base}{16})(\stackrel{height}{15}) \right]}~~ + ~~\stackrel{two~rectangles}{2(20)(17)}~~ + ~~\stackrel{one~rectangle}{(20)(16)} \\\\\\ 240~~ + ~~680~~ + ~~320\implies \text{\LARGE 1240}](https://img.qammunity.org/2023/formulas/mathematics/high-school/495btxgrow160l5ch0hl8n78cm9fq744rq.png)