Sabrina left home at 11.40 a.m. and drove towards the town. 2 hours later, her older brother left their home and drove towards the same town at 90 km/h. When the older brother reached the town at 5.40 p.m., Sabrina had another 6 km to travel. What was Sabrina’s average speed? Express your answer in mixed number.
Time that the Sabrina's older brother started driving = 1.40 p.m.
Duration that Sabrina's older brother drove from 1.40 p.m. to 5.40 p.m. = 4 h

Distance that Sabrina's older brother travelled
= 4 x 90
= 360 km

Distance that Sabrina travelled by the time her older brother reached the city
= 360 - 6
= 354 km

Time that Sabrina took to travel 354 km = 6 h

Sabrina's average speed
= 354 ÷ 6
= 59 km/h

Answer(s): 59 km/h