Sabrina left home at 11.45 a.m. and drove towards the campsite. 2 hours later, her older brother left their home and drove towards the same campsite at 79 km/h. When the older brother reached the campsite at 6.45 p.m., Sabrina had another 3 km to travel. What was Sabrina’s average speed? Express your answer in mixed number.
Time that the Sabrina's older brother started driving = 1.45 p.m.
Duration that Sabrina's older brother drove from 1.45 p.m. to 6.45 p.m. = 5 h

Distance that Sabrina's older brother travelled
= 5 x 79
= 395 km

Distance that Sabrina travelled by the time her older brother reached the city
= 395 - 3
= 392 km

Time that Sabrina took to travel 392 km = 7 h

Sabrina's average speed
= 392 ÷ 7
= 56 km/h

Answer(s): 56 km/h