Emma left home at 10.40 a.m. and drove towards the countryside. 3 hours later, her grandfather left their home and drove towards the same countryside at 100 km/h. When the grandfather reached the countryside at 6.40 p.m., Emma had another 6 km to travel. What was Emma’s average speed? Express your answer in mixed number.
Time that the Emma's grandfather started driving = 1.40 p.m.
Duration that Emma's grandfather drove from 1.40 p.m. to 6.40 p.m. = 5 h

Distance that Emma's grandfather travelled
= 5 x 100
= 500 km

Distance that Emma travelled by the time her grandfather reached the city
= 500 - 6
= 494 km

Time that Emma took to travel 494 km = 8 h

Emma's average speed
= 494 ÷ 8
= 61³₄ km/h

Answer(s): 61³₄ km/h