The formula for the surface area of a triangular prism can be completed as follows:
The surface area of a triangular prism is
\[ S.A. = \text{Base Area} + (S1 + S2 + S3) \cdot \text{Height} \]
Where:
- The base area is the area of the triangular base.
- \( S1, S2, \) and \( S3 \) are the lengths of the sides of the triangle.
- The height refers to the length of the prism, which connects the two triangular bases.
Thus, the completed formula is:
\[ S.A. = \text{Base Area} + (S1 + S2 + S3) \cdot \text{Height} \]