Answer:
![36+15+15+15+15](https://img.qammunity.org/2021/formulas/mathematics/college/oaoz1v1t0vmwtqkaycl269x4hfmthqr2dn.png)
Explanation:
For the surface area we need to add up all the areas in the pyramid:
- area of the triangle sides (there are 4 triangles)
Area of the base:
the base is a square, and the area of a square is given by:
![a_(base)=l^2](https://img.qammunity.org/2021/formulas/mathematics/college/7k49abbeyz5p01gr9eb09eaojisd2riwro.png)
where
is the length of the side:
, thus:
![a_(base)=(6)^2\\a_(base)=36](https://img.qammunity.org/2021/formulas/mathematics/college/cbsey5l0wm0qhtmr0vi556s60cjf88m6k2.png)
Area of the triangles:
one triangle has the area given by the formula:
![a_(triangle)=(b*h)/(2)](https://img.qammunity.org/2021/formulas/mathematics/middle-school/jt8d79mc2kbtk66d6v1cofgfo1ikj5jhs7.png)
where
is the base of the triangle:
![b=6](https://img.qammunity.org/2021/formulas/mathematics/college/28mt0m5c5guv1lxkxu5trptqjxf4v3oqgq.png)
and
is the height of the triangle:
, thus we have the following:
![a_(triangle)=(6*5)/(2) \\\\a_(triangle)=(30)/(2) \\\\a_(triangle)=15](https://img.qammunity.org/2021/formulas/mathematics/college/mhosmbjvbp6b7rcgw6hraqwm36w5p1eedd.png)
the expression that represents the surface area of the pyramid is:
![a_(base)+area_(triangle)+area_(triangle)+area_(triangle)+area_(triangle)](https://img.qammunity.org/2021/formulas/mathematics/college/9s4n9oik4w0dv34iz6bh59pva6qdor9czg.png)
substituting our values:
![36+15+15+15+15](https://img.qammunity.org/2021/formulas/mathematics/college/oaoz1v1t0vmwtqkaycl269x4hfmthqr2dn.png)
which is option B