Lucy left home at 10.30 a.m. and drove towards the city. 3 hours later, her grandmother left their home and drove towards the same city at 92 km/h. When the grandmother reached the city at 6.30 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 grandmother started driving = 1.30 p.m.
Duration that Lucy's grandmother drove from 1.30 p.m. to 6.30 p.m. = 5 h

Distance that Lucy's grandmother travelled
= 5 x 92
= 460 km

Distance that Lucy travelled by the time her grandmother reached the city
= 460 - 4
= 456 km

Time that Lucy took to travel 456 km = 8 h

Lucy's average speed
= 456 ÷ 8
= 57 km/h

Answer(s): 57 km/h