The surface area of a triangular prism is given by the formula:
\[ S.A. = (base \times height) + (S_1 + S_2 + S_3) \]
Here, \( S_1, S_2, \) and \( S_3 \) represent the areas of the three rectangular faces of the prism, which are formed from the sides of the triangular base, and the first part represents the area of the triangular base. For clarity, \( base \) and \( height \) would specifically refer to the dimensions of the triangular base.
Typically, the full formula could also be expressed as:
\[ S.A. = \text{Area of the triangular base} + \text{Perimeter of triangular base} \times \text{length of the prism} \]
However, based on your provided structure, the correct completion would be as follows:
\[ S.A. = ( \text{Area of the triangular base} ) + (S_1 + S_2 + S_3) \]
Just ensure you replace "base" and "height" with the corresponding values for your specific triangle.