Opal left home at 11.50 a.m. and drove towards the province. 2 hours later, her grandfather left their home and drove towards the same province at 84 km/h. When the grandfather reached the province at 5.50 p.m., Opal had another 3 km to travel. What was Opal’s average speed? Express your answer in mixed number.
Time that the Opal's grandfather started driving = 1.50 p.m.
Duration that Opal's grandfather drove from 1.50 p.m. to 5.50 p.m. = 4 h

Distance that Opal's grandfather travelled
= 4 x 84
= 336 km

Distance that Opal travelled by the time her grandfather reached the city
= 336 - 3
= 333 km

Time that Opal took to travel 333 km = 6 h

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

Answer(s): 55¹₂ km/h