At 13 30, Billy left Town Z for Town A, driving at a speed of 85 km/h. At 16 30, Warren also left Town Z for Town A driving at a certain speed. Both of them did not change their speed throughout the journey. At 19 30, both of them passed a grocery store that was 255 km away from Town A. How many minutes earlier did Warren reach Town A than Billy?

Distance that Billy travelled
= 6 x 85
= 510 km

Distance between Town Z and Town A
= 510 + 255
= 765 km

Since Warren passed the grocery store at the same time as Billy, it means that Warren travelled 510 km in 3 hours.

Warren's speed during the journey
= 510 ÷ 3
= 170 km/h

Duration that Warren took to reach Town A after passing the grocery store
= 255 ÷ 170
= 1.5 h

Duration that Billy took to reach Town A after passing the grocery store
= 255 ÷ 85
= 3 h

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

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

Warren reached Town A 90 minutes earlier than Billy.

Answer(s): 90 min