Gem left home at 10.25 a.m. and drove towards the countryside. 3 hours later, her cousin left their home and drove towards the same countryside at 85 km/h. When the cousin reached the countryside at 6.25 p.m., Gem had another 5 km to travel. What was Gem’s average speed? Express your answer in mixed number.
Time that the Gem's cousin started driving = 1.25 p.m.
Duration that Gem's cousin drove from 1.25 p.m. to 6.25 p.m. = 5 h

Distance that Gem's cousin travelled
= 5 x 85
= 425 km

Distance that Gem travelled by the time her cousin reached the city
= 425 - 5
= 420 km

Time that Gem took to travel 420 km = 8 h

Gem's average speed
= 420 ÷ 8
= 52¹₂ km/h

Answer(s): 52¹₂ km/h