1. **Problem statement:** Given parallelogram ABCD with points A(-11, 21), B(-14, 28), and C(6, 24), find the coordinates of point D. 2. **Formula and properties:** In a parallelogram, the diagonals bisect each other. This means the midpoint of diagonal AC is the same as the midpoint of diagonal BD. 3. **Calculate midpoint of AC:** $$\text{Midpoint}_{AC} = \left(\frac{-11 + 6}{2}, \frac{21 + 24}{2}\right) = \left(\frac{-5}{2}, \frac{45}{2}\right) = (-2.5, 22.5)$$ 4. **Let coordinates of D be $(x, y)$. Calculate midpoint of BD:** $$\text{Midpoint}_{BD} = \left(\frac{-14 + x}{2}, \frac{28 + y}{2}\right)$$ 5. **Set midpoints equal:** $$\left(\frac{-14 + x}{2}, \frac{28 + y}{2}\right) = (-2.5, 22.5)$$ 6. **Solve for $x$ and $y$:** $$\frac{-14 + x}{2} = -2.5 \implies -14 + x = -5 \implies x = -5 + 14 = 9$$ $$\frac{28 + y}{2} = 22.5 \implies 28 + y = 45 \implies y = 45 - 28 = 17$$ 7. **Answer:** The coordinates of point D are $(9, 17)$.