Olivia left home at 11.25 a.m. and drove towards the suburb. 2 hours later, her older brother left their home and drove towards the same suburb at 93 km/h. When the older brother reached the suburb at 4.25 p.m., Olivia had another 4 km to travel. What was Olivia’s average speed? Express your answer in mixed number.
Time that the Olivia's older brother started driving = 1.25 p.m.
Duration that Olivia's older brother drove from 1.25 p.m. to 4.25 p.m. = 3 h

Distance that Olivia's older brother travelled
= 3 x 93
= 279 km

Distance that Olivia travelled by the time her older brother reached the city
= 279 - 4
= 275 km

Time that Olivia took to travel 275 km = 5 h

Olivia's average speed
= 275 ÷ 5
= 55 km/h

Answer(s): 55 km/h