The single transformation that maps triangle A onto triangle C is a **rotation of 180 degrees around a point that is offset from the origin by the translation vector (-3, 1)**.
Here's how we can arrive at this answer:
1. **Translation:** Triangle A is first translated by the vector (-3, 1), which moves each point of the triangle 3 units to the left and 1 unit up. This results in triangle B.
2. **Rotation:** Triangle B is then rotated 180 degrees around a fixed point. Since the final triangle, C, is the mirror image of A across the vertical axis, this fixed point must be offset from the origin by the translation vector.
3. **Combined Transformation:** Therefore, the single transformation that achieves the same result as the two separate steps is a 180-degree rotation around a point that is 3 units to the left and 1 unit up from the origin.
In other words, imagine fixing a point at (-3, 1) and then placing a sheet of paper with triangle A on top of it. Rotating the paper 180 degrees around this point will make triangle A coincide with triangle C.