Lucy left home at 11.10 a.m. and drove towards the suburb. 3 hours later, her younger brother left their home and drove towards the same suburb at 86 km/h. When the younger brother reached the suburb at 7.10 p.m., Lucy had another 4 km to travel. What was Lucy’s average speed? Express your answer in mixed number.
Time that the Lucy's younger brother started driving = 2.10 p.m.
Duration that Lucy's younger brother drove from 2.10 p.m. to 7.10 p.m. = 5 h

Distance that Lucy's younger brother travelled
= 5 x 86
= 430 km

Distance that Lucy travelled by the time her younger brother reached the city
= 430 - 4
= 426 km

Time that Lucy took to travel 426 km = 8 h

Lucy's average speed
= 426 ÷ 8
= 53¹₄ km/h

Answer(s): 53¹₄ km/h