At 11 50, Zane left Town Y for Town Z, driving at a speed of 90 km/h. At 13 50, Ahmad also left Town Y for Town Z driving at a certain speed. Both of them did not change their speed throughout the journey. At 16 50, both of them passed a library that was 180 km away from Town Z. How many minutes earlier did Ahmad reach Town Z than Zane?

Distance that Zane travelled
= 5 x 90
= 450 km

Distance between Town Y and Town Z
= 450 + 180
= 630 km

Since Ahmad passed the library at the same time as Zane, it means that Ahmad travelled 450 km in 3 hours.

Ahmad's speed during the journey
= 450 ÷ 3
= 150 km/h

Duration that Ahmad took to reach Town Z after passing the library
= 180 ÷ 150
= 1.2 h

Duration that Zane took to reach Town Z after passing the library
= 180 ÷ 90
= 2 h

Difference between the time they took to reach Town Z
= 2 - 1.2
= 0.8 h

1 h = 60 min
0.8 h = 0.8 x 60 = 48 min

Ahmad reached Town Z 48 minutes earlier than Zane.

Answer(s): 48 min