you have to find the areas of the triangle faces and rectangular faces, so…
the triangles' areas are:
6 • 16 = 96
the rectangles on the sides have areas of:
10 • 9 • 2 = 180
and the base rectangle has an area of
16 • 9 = 144
the surface area is 96+180+144 which is 420 in2.
