Xuan left home at 11.45 a.m. and drove towards the suburb. 2 hours later, her mother left their home and drove towards the same suburb at 89 km/h. When the mother reached the suburb at 6.45 p.m., Xuan had another 4 km to travel. What was Xuan’s average speed? Express your answer in mixed number.
Time that the Xuan's mother started driving = 1.45 p.m.
Duration that Xuan's mother drove from 1.45 p.m. to 6.45 p.m. = 5 h

Distance that Xuan's mother travelled
= 5 x 89
= 445 km

Distance that Xuan travelled by the time her mother reached the city
= 445 - 4
= 441 km

Time that Xuan took to travel 441 km = 7 h

Xuan's average speed
= 441 ÷ 7
= 63 km/h

Answer(s): 63 km/h