Point T is at (–16.8, 31.7) and point M is at (1.2, 12.5). Point M is the midpoint of the line segment whose endpoints are S and T.

For a midpoint, each coordinate is the average of the endpoints, so the missing endpoint S has coordinates S = 2M − T. Calculate x: 2(1.2) − (−16.8) = 19.2; calculate y: 2(12.5) − 31.7 = −6.7. Thus S is (19.2, −6.7), choice C.

AI-written and checked against the verified answer.