Roshel left home at 10.20 a.m. and drove towards the city. 3 hours later, her younger brother left their home and drove towards the same city at 91 km/h. When the younger brother reached the city at 6.20 p.m., Roshel had another 3 km to travel. What was Roshel’s average speed? Express your answer in mixed number.
Time that the Roshel's younger brother started driving = 1.20 p.m.
Duration that Roshel's younger brother drove from 1.20 p.m. to 6.20 p.m. = 5 h

Distance that Roshel's younger brother travelled
= 5 x 91
= 455 km

Distance that Roshel travelled by the time her younger brother reached the city
= 455 - 3
= 452 km

Time that Roshel took to travel 452 km = 8 h

Roshel's average speed
= 452 ÷ 8
= 56¹₂ km/h

Answer(s): 56¹₂ km/h