Yen left home at 11.25 a.m. and drove towards the suburb. 2 hours later, her grandfather left their home and drove towards the same suburb at 86 km/h. When the grandfather reached the suburb at 5.25 p.m., Yen had another 5 km to travel. What was Yen’s average speed? Express your answer in mixed number.
Time that the Yen's grandfather started driving = 1.25 p.m.
Duration that Yen's grandfather drove from 1.25 p.m. to 5.25 p.m. = 4 h

Distance that Yen's grandfather travelled
= 4 x 86
= 344 km

Distance that Yen travelled by the time her grandfather reached the city
= 344 - 5
= 339 km

Time that Yen took to travel 339 km = 6 h

Yen's average speed
= 339 ÷ 6
= 56¹₂ km/h

Answer(s): 56¹₂ km/h