At 14 20, Riordan left Town D for Town E, driving at a speed of 64 km/h. At 16 20, Billy also left Town D for Town E driving at a certain speed. Both of them did not change their speed throughout the journey. At 18 20, both of them passed a library that was 192 km away from Town E. How many minutes earlier did Billy reach Town E than Riordan?

Distance that Riordan travelled
= 4 x 64
= 256 km

Distance between Town D and Town E
= 256 + 192
= 448 km

Since Billy passed the library at the same time as Riordan, it means that Billy travelled 256 km in 2 hours.

Billy's speed during the journey
= 256 ÷ 2
= 128 km/h

Duration that Billy took to reach Town E after passing the library
= 192 ÷ 128
= 1.5 h

Duration that Riordan took to reach Town E after passing the library
= 192 ÷ 64
= 3 h

Difference between the time they took to reach Town E
= 3 - 1.5
= 1.5 h

1 h = 60 min
1.5 h = 1.5 x 60 = 90 min

Billy reached Town E 90 minutes earlier than Riordan.

Answer(s): 90 min