Wendy left home at 11.45 a.m. and drove towards the countryside. 3 hours later, her older brother left their home and drove towards the same countryside at 84 km/h. When the older brother reached the countryside at 7.45 p.m., Wendy had another 4 km to travel. What was Wendy’s average speed? Express your answer in mixed number.
Time that the Wendy's older brother started driving = 2.45 p.m.
Duration that Wendy's older brother drove from 2.45 p.m. to 7.45 p.m. = 5 h

Distance that Wendy's older brother travelled
= 5 x 84
= 420 km

Distance that Wendy travelled by the time her older brother reached the city
= 420 - 4
= 416 km

Time that Wendy took to travel 416 km = 8 h

Wendy's average speed
= 416 ÷ 8
= 52 km/h

Answer(s): 52 km/h