Answer:
-19.0 kJ
Explanation:
Let's keep in mind that the direction of the resistive force is always opposite to the displacement of the bicyclist.
- In the first part of the ride:
Displacement: d = 1.86 km = 1860 m
Resistive force: F = 5.12 N
Angle between the direction of the force and the displacement: 
So, the work done by the resistive force is

- Similarly, in the second part of the ride:
Displacement: d = 1.86 km = 1860 m
Resistive force: F = 5.12 N
Angle between the direction of the force and the displacement: 
So, the work done by the resistive force is

Therefore, the total work done by the resistive force during the round trip is
