Answer:
S.A. = 297 mm²
Step-by-step explanation:
We have a square in the base and four triangles on the lateral surface.
The formula of an area of a square:
[tex]A_{\square}=s^2[/tex]
s - side
We have s = 9mm. Susbtitute:
[tex]A_{\square}=9^2=81\ mm^2[/tex]
The formula of an area of a triangle:
[tex]A_{\triangle}=\dfrac{bh}{2}[/tex]
b - base
h - height
We have b = 9 mm and h = 12 mm. Substitute:
[tex]A_{\triangle}=\dfrac{(9)(12)}{2}=54\ mm^2[/tex]
The Surface Area:
[tex]S.A.=A_{\square}+4A_{\triangle}[/tex]
Substitute:
[tex]S.A.=81+4(54)=297\ mm^2[/tex]
