A bus leaves a stop and speeds up steadily for 10 s to 15 m/s…

Step 1. (a) A line rising from $0\ \text{m/s}$ to $15\ \text{m/s}$ in $10\ \text{s}$, flat for $20\ \text{s}$, falling to $0\ \text{m/s}$ in $10\ \text{s}$.

Step 2. (b) $\dfrac{15\ \text{m/s}}{10\ \text{s}} = 1.5\ \text{m/s}^2$; then $0\ \text{m/s}^2$; then $\dfrac{0\ \text{m/s} - 15\ \text{m/s}}{10\ \text{s}} = -1.5\ \text{m/s}^2$.

Step 3. (c) $\tfrac12 \times 10\ \text{s} \times 15\ \text{m/s} + 20\ \text{s} \times 15\ \text{m/s} + \tfrac12 \times 10\ \text{s} \times 15\ \text{m/s} = 75\ \text{m} + 300\ \text{m} + 75\ \text{m} = 450\ \text{m}$.