Mary left home at 10.20 a.m. and drove towards the campsite. 3 hours later, her uncle left their home and drove towards the same campsite at 86 km/h. When the uncle reached the campsite at 6.20 p.m., Mary had another 4 km to travel. What was Mary’s average speed? Express your answer in mixed number.
Time that the Mary's uncle started driving = 1.20 p.m.
Duration that Mary's uncle drove from 1.20 p.m. to 6.20 p.m. = 5 h

Distance that Mary's uncle travelled
= 5 x 86
= 430 km

Distance that Mary travelled by the time her uncle reached the city
= 430 - 4
= 426 km

Time that Mary took to travel 426 km = 8 h

Mary's average speed
= 426 ÷ 8
= 53¹₄ km/h

Answer(s): 53¹₄ km/h