Esther left home at 10.55 a.m. and drove towards the city. 3 hours later, her younger sister left their home and drove towards the same city at 100 km/h. When the younger sister reached the city at 6.55 p.m., Esther had another 4 km to travel. What was Esther’s average speed? Express your answer in mixed number.
Time that the Esther's younger sister started driving = 1.55 p.m.
Duration that Esther's younger sister drove from 1.55 p.m. to 6.55 p.m. = 5 h

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

Distance that Esther travelled by the time her younger sister reached the city
= 500 - 4
= 496 km

Time that Esther took to travel 496 km = 8 h

Esther's average speed
= 496 ÷ 8
= 62 km/h

Answer(s): 62 km/h