The first step is to find the relationship between the square base and the surface area.
Surface area (SA) = area of the square (SS) + area of triangles.4(AT)
Thus we can conclude area of triangles 4(AT) = SA - SS = 864 - (18*18)
4(AT) = 864 - 324 = 540
Each triangle = 540/4 = 135 square in.
An area of one triangle (AT)= (base* slant height)/2
The base = 18 in.
slant height = 2(AT)/base = 2(135)/18 = 15
