Explanation:
the total surface area is the sum of the individual areas.
we have the ground area : a 6×6 square. = 36 cm²
and we have 4 equal triangles.
the area of a triangle is baseline × height / 2.
which is for each of these triangles
6 × 12 / 2 = 3 × 12 = 36 cm²
so, the total surface area of the pyramid is
36 + 4×36 = 5×36 = 180 cm²