Victoria started jogging from the grocery store to the nature reserve at a speed of 105 m/min at 6 a.m. Her cousin started jogging from the grocery store later. They were beside each other at 6.36 a.m. and her cousin reached the nature reserve at 7 a.m. while Victoria was still 1800 m away. If both of them travelled at a constant speed throughout the journey, what time did her cousin leave the grocery store?
1 h = 60 min

From 6 a.m. to 7 a.m. = 1 h
From 6.36 a.m. to 7 a.m. = 24 min

Distance between the grocery store and the nature reserve
= 60 x 105 + 1800
= 6300 + 1800
= 8100 m

Distance that Victoria's cousin had to cover to catch up with Victoria
= 36 x 105
= 3780 m

Distance that Victoria's cousin travelled to the nature reserve after catching up with Victoria
= 8100 - 3780
= 4320 m

Since Victoria's cousin jogged 4320 m in 36 min,
Victoria's cousin average speed
= 4320 ÷ 24
= 180 m/min

Duration that Victoria's cousin took to jog to the nature reserve
= 8100 ÷ 180
= 45 min

Time that Victoria's cousin left the grocery store:
45 min before 7 a.m. = 6.15 a.m.

Answer(s): 6.15 a.m.