Penelope left home at 11.45 a.m. and drove towards the campsite. 3 hours later, her older brother left their home and drove towards the same campsite at 86 km/h. When the older brother reached the campsite at 7.45 p.m., Penelope had another 2 km to travel. What was Penelope’s average speed? Express your answer in mixed number.
Time that the Penelope's older brother started driving = 2.45 p.m.
Duration that Penelope's older brother drove from 2.45 p.m. to 7.45 p.m. = 5 h

Distance that Penelope's older brother travelled
= 5 x 86
= 430 km

Distance that Penelope travelled by the time her older brother reached the city
= 430 - 2
= 428 km

Time that Penelope took to travel 428 km = 8 h

Penelope's average speed
= 428 ÷ 8
= 53¹₂ km/h

Answer(s): 53¹₂ km/h