Sarah left home at 11.30 a.m. and drove towards the seaside resort. 2 hours later, her mother left their home and drove towards the same seaside resort at 85 km/h. When the mother reached the seaside resort at 6.30 p.m., Sarah had another 5 km to travel. What was Sarah’s average speed? Express your answer in mixed number.
Time that the Sarah's mother started driving = 1.30 p.m.
Duration that Sarah's mother drove from 1.30 p.m. to 6.30 p.m. = 5 h

Distance that Sarah's mother travelled
= 5 x 85
= 425 km

Distance that Sarah travelled by the time her mother reached the city
= 425 - 5
= 420 km

Time that Sarah took to travel 420 km = 7 h

Sarah's average speed
= 420 ÷ 7
= 60 km/h

Answer(s): 60 km/h