Opal left home at 10.40 a.m. and drove towards the campsite. 3 hours later, her father left their home and drove towards the same campsite at 92 km/h. When the father reached the campsite at 6.40 p.m., Opal had another 4 km to travel. What was Opal’s average speed? Express your answer in mixed number.
Time that the Opal's father started driving = 1.40 p.m.
Duration that Opal's father drove from 1.40 p.m. to 6.40 p.m. = 5 h

Distance that Opal's father travelled
= 5 x 92
= 460 km

Distance that Opal travelled by the time her father reached the city
= 460 - 4
= 456 km

Time that Opal took to travel 456 km = 8 h

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

Answer(s): 57 km/h