Time and Speed puzzle

Two friends decided to get together and start riding bikes towards each other, both at a speed of 6 km/hr (starting at the same time). The live 36 km apart and hence will meet halfway.
One of them have a pet pigeon and it starts flying the instant the friends start traveling. The pigeon flies back and forth between the two friends, at a speed of 18 km/hr until the friends meet.
How much distance (in km) will the pigeon travel?

Solution:

The time for which pigeon will fly is equal to the time taken by friends to meet (after they start from their homes).

Relative speed of friends = 6 + 6 = 12 km/hr (traveling toward each other)

Distance = 36 km

Time taken to meet = 36/12 = 3 hrs.

Pigeon is flying at a speed of 18 km/hr.

In 3 hrs it will cover a distance of 18 * 3 = 54 km.