Joelle left home at 11.45 a.m. and drove towards the campsite. 2 hours later, her younger sister left their home and drove towards the same campsite at 84 km/h. When the younger sister reached the campsite at 5.45 p.m., Joelle had another 3 km to travel. What was Joelle’s average speed? Express your answer in mixed number.
Time that the Joelle's younger sister started driving = 1.45 p.m.
Duration that Joelle's younger sister drove from 1.45 p.m. to 5.45 p.m. = 4 h

Distance that Joelle's younger sister travelled
= 4 x 84
= 336 km

Distance that Joelle travelled by the time her younger sister reached the city
= 336 - 3
= 333 km

Time that Joelle took to travel 333 km = 6 h

Joelle's average speed
= 333 ÷ 6
= 55¹₂ km/h

Answer(s): 55¹₂ km/h