The graph shows the position of a student walking along a straight road, measured from her house.

Step 1. (a) A: $\dfrac{20\ \text{m}}{10\ \text{s}} = 2\ \text{m/s}$. B: $0\ \text{m/s}$. C: $\dfrac{30\ \text{m}}{10\ \text{s}} = 3\ \text{m/s}$. D: $\dfrac{10\ \text{m} - 50\ \text{m}}{20\ \text{s}} = -2\ \text{m/s}$, back towards home.

Step 2. (b) Part B, where the line is flat.

Step 3. (c) Distance $20\ \text{m} + 0\ \text{m} + 30\ \text{m} + 40\ \text{m} = 90\ \text{m}$; displacement $10\ \text{m}$ from the house.

Step 4. (d) $\dfrac{90\ \text{m}}{50\ \text{s}} = 1.8\ \text{m/s}$.