Answer:
D. 96 m²
Explanation:
The surface area of a triangular prism is the sum of the areas of all of the faces. A triangular prism has two triangular faces (bases) and three rectangular faces.
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rectangular faces
The dimensions of the rectangular faces are such that they can be considered together as a rectangle whose width is the distance between the triangular faces, and whose length is the perimeter of the triangle. For this prism, that is a 7 m width and a (3+4+5) = 12 m length.
triangular faces
The two triangular faces together have an area that is equal to that of a rectangle with the same base and height as the triangular face. For this prism, that is a 3 m base and a 4 m height.
total
The total surface area is ...
lateral area + base area = (7 m)(12 m) +(3 m)(4 m) = (84 +12) m²
surface area = 96 m²
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Additional comment
The formula for the area of a triangle is ...
A = 1/2bh
A triangular prism has two congruent triangular faces, so their total area is ...
A = 2(1/2bh) = bh
We elected to skip the halving and doubling, and go straight to the total base area.