Esther left home at 11.45 a.m. and drove towards the countryside. 3 hours later, her grandmother left their home and drove towards the same countryside at 100 km/h. When the grandmother reached the countryside at 7.45 p.m., Esther had another 6 km to travel. What was Esther’s average speed? Express your answer in mixed number.
Time that the Esther's grandmother started driving = 2.45 p.m.
Duration that Esther's grandmother drove from 2.45 p.m. to 7.45 p.m. = 5 h

Distance that Esther's grandmother travelled
= 5 x 100
= 500 km

Distance that Esther travelled by the time her grandmother reached the city
= 500 - 6
= 494 km

Time that Esther took to travel 494 km = 8 h

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

Answer(s): 61³₄ km/h