Gem left home at 11.15 a.m. and drove towards the city. 3 hours later, her grandfather left their home and drove towards the same city at 92 km/h. When the grandfather reached the city at 7.15 p.m., Gem had another 6 km to travel. What was Gem’s average speed? Express your answer in mixed number.
Time that the Gem's grandfather started driving = 2.15 p.m.
Duration that Gem's grandfather drove from 2.15 p.m. to 7.15 p.m. = 5 h

Distance that Gem's grandfather travelled
= 5 x 92
= 460 km

Distance that Gem travelled by the time her grandfather reached the city
= 460 - 6
= 454 km

Time that Gem took to travel 454 km = 8 h

Gem's average speed
= 454 ÷ 8
= 56³₄ km/h

Answer(s): 56³₄ km/h