Xuan left home at 11.15 a.m. and drove towards the city. 2 hours later, her younger brother left their home and drove towards the same city at 82 km/h. When the younger brother reached the city at 6.15 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 younger brother started driving = 1.15 p.m.
Duration that Xuan's younger brother drove from 1.15 p.m. to 6.15 p.m. = 5 h

Distance that Xuan's younger brother travelled
= 5 x 82
= 410 km

Distance that Xuan travelled by the time her younger brother reached the city
= 410 - 4
= 406 km

Time that Xuan took to travel 406 km = 7 h

Xuan's average speed
= 406 ÷ 7
= 58 km/h

Answer(s): 58 km/h