Answer :
To obtain the surface area of a triangular prism, the formula to employ is:
[tex]\begin{gathered} A_{triangular\text{ prism}}=2A_B+(a+b+c)h \\ \text{where A}_B=\sqrt[]{s(s-a)(s-b)(s-c)} \\ \text{where s=}\frac{a+b+c}{2} \\ a,b\text{ and c are sides of the triangular prism and h is the height} \end{gathered}[/tex]From the image, a=18in, b=21in, c =15in and h=12in
We have to obtain the value of 's' first, from the equation:
[tex]\begin{gathered} s=\frac{a+b+c}{2} \\ s=\frac{18+21+15}{2} \\ s=\frac{54}{2} \\ s=27in \end{gathered}[/tex][tex]\begin{gathered} \text{Then, we obtain the value of A}_B \\ A_B=\sqrt[]{s(s-a)(s-b)(s-c)} \\ A_B=\sqrt[]{27(27-18)(27-21)(27-15)} \\ A_B=\sqrt[]{27(9)(6)(12)} \\ A_B=\sqrt[]{17496} \\ A_B=132.27in^2 \end{gathered}[/tex]The final step is to obtain the area of the triangular, having gotten the values needed to be inputted in the formula;
[tex]\begin{gathered} A_{triangular\text{ prism}}=2A_B+(a+b+c)h \\ A_{triangular\text{ prism}}=(2\times132.27)+(18+21+15)12 \\ A_{triangular\text{ prism}}=264.54+(54)12 \\ A_{triangular\text{ prism}}=264.54+648 \\ A_{triangular\text{ prism}}=912.54in^2 \end{gathered}[/tex]Hence, the surface area of the triangular prism is 912.54 square inches
