Emma left home at 11.50 a.m. and drove towards the suburb. 3 hours later, her grandmother left their home and drove towards the same suburb at 92 km/h. When the grandmother reached the suburb at 7.50 p.m., Emma had another 4 km to travel. What was Emma’s average speed? Express your answer in mixed number.
Time that the Emma's grandmother started driving = 2.50 p.m.
Duration that Emma's grandmother drove from 2.50 p.m. to 7.50 p.m. = 5 h

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

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

Time that Emma took to travel 456 km = 8 h

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

Answer(s): 57 km/h