Find the area of the polygon.

The formula for the area of the triangles is base x hight divided by 2 (bh/2)
The formula for the square is length times width (l x w)

therefore...

bh/2 = (12)(6) / 2 = 36 (this is the area of one triangle)

then you need to times 36 by 4 because you have 4 triangles.
36 x 4 = 144

l x w = 12 x 12 = 144 (this is the area of the square)

last you need to add the area of the triangles (144) and the area of the square (144) because that will give you the total surface area of the shape.

144+144= 288

so your answer is 288cm squared (288cm2)