Opal left home at 10.25 a.m. and drove towards the countryside. 3 hours later, her grandfather left their home and drove towards the same countryside at 91 km/h. When the grandfather reached the countryside at 6.25 p.m., Opal had another 5 km to travel. What was Opal’s average speed? Express your answer in mixed number.
Time that the Opal's grandfather started driving = 1.25 p.m.
Duration that Opal's grandfather drove from 1.25 p.m. to 6.25 p.m. = 5 h

Distance that Opal's grandfather travelled
= 5 x 91
= 455 km

Distance that Opal travelled by the time her grandfather reached the city
= 455 - 5
= 450 km

Time that Opal took to travel 450 km = 8 h

Opal's average speed
= 450 ÷ 8
= 56¹₄ km/h

Answer(s): 56¹₄ km/h