Dana left home at 10.30 a.m. and drove towards the campsite. 3 hours later, her grandmother left their home and drove towards the same campsite at 90 km/h. When the grandmother reached the campsite at 6.30 p.m., Dana had another 4 km to travel. What was Dana’s average speed? Express your answer in mixed number.
Time that the Dana's grandmother started driving = 1.30 p.m.
Duration that Dana's grandmother drove from 1.30 p.m. to 6.30 p.m. = 5 h

Distance that Dana's grandmother travelled
= 5 x 90
= 450 km

Distance that Dana travelled by the time her grandmother reached the city
= 450 - 4
= 446 km

Time that Dana took to travel 446 km = 8 h

Dana's average speed
= 446 ÷ 8
= 55³₄ km/h

Answer(s): 55³₄ km/h