Wendy left home at 11.30 a.m. and drove towards the town. 2 hours later, her younger brother left their home and drove towards the same town at 78 km/h. When the younger brother reached the town at 6.30 p.m., Wendy had another 5 km to travel. What was Wendy’s average speed? Express your answer in mixed number.
Time that the Wendy's younger brother started driving = 1.30 p.m.
Duration that Wendy's younger brother drove from 1.30 p.m. to 6.30 p.m. = 5 h

Distance that Wendy's younger brother travelled
= 5 x 78
= 390 km

Distance that Wendy travelled by the time her younger brother reached the city
= 390 - 5
= 385 km

Time that Wendy took to travel 385 km = 7 h

Wendy's average speed
= 385 ÷ 7
= 55 km/h

Answer(s): 55 km/h