1. **State the problem:** We are given a midpoint of a line segment and one endpoint, and we need to find the other endpoint. 2. **Formula used:** The midpoint $M$ of a segment with endpoints $A(x_1,y_1)$ and $B(x_2,y_2)$ is given by $$M = \left(\frac{x_1+x_2}{2}, \frac{y_1+y_2}{2}\right)$$ 3. **Given values:** - Midpoint $M = (12,7)$ - One endpoint $A = (3,11)$ - Other endpoint $B = (x,y)$ (unknown) 4. **Set up equations:** $$12 = \frac{3 + x}{2}$$ $$7 = \frac{11 + y}{2}$$ 5. **Solve for $x$:** Multiply both sides by 2: $$2 \times 12 = 3 + x$$ $$24 = 3 + x$$ Subtract 3 from both sides: $$24 - 3 = x$$ $$x = 21$$ 6. **Solve for $y$:** Multiply both sides by 2: $$2 \times 7 = 11 + y$$ $$14 = 11 + y$$ Subtract 11 from both sides: $$14 - 11 = y$$ $$y = 3$$ 7. **Final answer:** The other stop sign is located at $(21,3)$. **Answer choice:** C. (21, 3)