ANSWER:
The total surface area is 450 mm^2
STEP-BY-STEP EXPLANATION:
We have a pyramid with a triangular base, which the formula to calculate the total surface area is the following
[tex]\begin{gathered} A_T=A_B+A_L \\ A_B=\frac{b\cdot h}{2} \\ A_L=3\cdot\frac{b\cdot l}{2} \end{gathered}[/tex]
Replacing:
[tex]\begin{gathered} A_T=\frac{20\cdot15}{2}+3\cdot\frac{20\cdot10}{2} \\ A_T=150+300 \\ A_T=450 \end{gathered}[/tex]
