I’m pretty sure it would be 0.1
Alright, we just need to reverse some operations done unto 43. Subtract the 15 from her collection.
43 - 15 = 28.
Sold half? Times half.
28 * 2 = 56
Make sure it works:
56 - 28 = 28. 28 + 15 = 43.
She had 56 cards to start with.
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.