At 10 50, Mark left Town Y for Town Z, driving at a speed of 79 km/h. At 12 50, David also left Town Y for Town Z driving at a certain speed. Both of them did not change their speed throughout the journey. At 14 50, both of them passed a playground that was 237 km away from Town Z. How many minutes earlier did David reach Town Z than Mark?

Distance that Mark travelled
= 4 x 79
= 316 km

Distance between Town Y and Town Z
= 316 + 237
= 553 km

Since David passed the playground at the same time as Mark, it means that David travelled 316 km in 2 hours.

David's speed during the journey
= 316 ÷ 2
= 158 km/h

Duration that David took to reach Town Z after passing the playground
= 237 ÷ 158
= 1.5 h

Duration that Mark took to reach Town Z after passing the playground
= 237 ÷ 79
= 3 h

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

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

David reached Town Z 90 minutes earlier than Mark.

Answer(s): 90 min