To solve part (a), we calculate Dave's average speed on his outward journey. Here's how:

From the graph:

• Outward journey starts at 2:00 PM and ends at 3:00 PM (1 hour).
• Distance traveled = 30 km.

Average speed = Total distance / Total time
= $\frac{30 \, \text{km}}{1 \, \text{hour}}$
= 30 km/h.

Do you want me to delve into parts (b) and (c) or expand further on this?

Here are 5 related questions for practice:

1. How would the average speed change if Dave took 2 hours for the outward journey?
2. What is the formula for calculating average speed over a round trip?
3. How does stopping time affect the calculation of overall average speed?
4. How can you determine the total distance traveled from such graphs?
5. How does slope represent speed on distance-time graphs?

Tip: In a distance-time graph, a steeper slope indicates a higher speed.