We need to find surface area, so we can imagine breaking it up into face net.
There will be 18 × 18 square base, four 18 × 40 rectangles, and four triangles with base 18 and height 13.
So the surface area would be sum of these areas.
That would be 18×18 + 4( 18 × 40 ) + 4( (1/2) 18×13 ) = 3672
Final answer: 3672 m²
Hope this helps.