1. **Problem (a):** Find the distance between points $A(3,4,5)$ and $B(6,8,9)$. 2. **Formula:** The distance between two points in 3D is given by $$\overline{AB} = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2 + (z_2 - z_1)^2}$$ 3. **Calculation:** Substitute the coordinates: $$\overline{AB} = \sqrt{(6-3)^2 + (8-4)^2 + (9-5)^2} = \sqrt{3^2 + 4^2 + 4^2} = \sqrt{9 + 16 + 16} = \sqrt{41}$$ 4. **Answer:** The distance $\overline{AB} = \sqrt{41}$ units.