Gillian left home at 11.20 a.m. and drove towards the campsite. 3 hours later, her older sister left their home and drove towards the same campsite at 92 km/h. When the older sister reached the campsite at 7.20 p.m., Gillian had another 4 km to travel. What was Gillian’s average speed? Express your answer in mixed number.
Time that the Gillian's older sister started driving = 2.20 p.m.
Duration that Gillian's older sister drove from 2.20 p.m. to 7.20 p.m. = 5 h

Distance that Gillian's older sister travelled
= 5 x 92
= 460 km

Distance that Gillian travelled by the time her older sister reached the city
= 460 - 4
= 456 km

Time that Gillian took to travel 456 km = 8 h

Gillian's average speed
= 456 ÷ 8
= 57 km/h

Answer(s): 57 km/h