Gillian left home at 11.45 a.m. and drove towards the city. 2 hours later, her grandfather left their home and drove towards the same city at 86 km/h. When the grandfather reached the city at 4.45 p.m., Gillian had another 3 km to travel. What was Gillian’s average speed? Express your answer in mixed number.
Time that the Gillian's grandfather started driving = 1.45 p.m.
Duration that Gillian's grandfather drove from 1.45 p.m. to 4.45 p.m. = 3 h

Distance that Gillian's grandfather travelled
= 3 x 86
= 258 km

Distance that Gillian travelled by the time her grandfather reached the city
= 258 - 3
= 255 km

Time that Gillian took to travel 255 km = 5 h

Gillian's average speed
= 255 ÷ 5
= 51 km/h

Answer(s): 51 km/h