Winnie left home at 11.25 a.m. and drove towards the countryside. 2 hours later, her older brother left their home and drove towards the same countryside at 87 km/h. When the older brother reached the countryside at 4.25 p.m., Winnie had another 6 km to travel. What was Winnie’s average speed? Express your answer in mixed number.
Time that the Winnie's older brother started driving = 1.25 p.m.
Duration that Winnie's older brother drove from 1.25 p.m. to 4.25 p.m. = 3 h

Distance that Winnie's older brother travelled
= 3 x 87
= 261 km

Distance that Winnie travelled by the time her older brother reached the city
= 261 - 6
= 255 km

Time that Winnie took to travel 255 km = 5 h

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

Answer(s): 51 km/h