Xuan left home at 11.35 a.m. and drove towards the province. 2 hours later, her father left their home and drove towards the same province at 79 km/h. When the father reached the province at 5.35 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 father started driving = 1.35 p.m.
Duration that Xuan's father drove from 1.35 p.m. to 5.35 p.m. = 4 h

Distance that Xuan's father travelled
= 4 x 79
= 316 km

Distance that Xuan travelled by the time her father reached the city
= 316 - 4
= 312 km

Time that Xuan took to travel 312 km = 6 h

Xuan's average speed
= 312 ÷ 6
= 52 km/h

Answer(s): 52 km/h