Opal left home at 10.10 a.m. and drove towards the town. 3 hours later, her grandmother left their home and drove towards the same town at 84 km/h. When the grandmother reached the town at 6.10 p.m., Opal had another 2 km to travel. What was Opal’s average speed? Express your answer in mixed number.
Time that the Opal's grandmother started driving = 1.10 p.m.
Duration that Opal's grandmother drove from 1.10 p.m. to 6.10 p.m. = 5 h

Distance that Opal's grandmother travelled
= 5 x 84
= 420 km

Distance that Opal travelled by the time her grandmother reached the city
= 420 - 2
= 418 km

Time that Opal took to travel 418 km = 8 h

Opal's average speed
= 418 ÷ 8
= 52¹₄ km/h

Answer(s): 52¹₄ km/h