Usha left home at 10.55 a.m. and drove towards the town. 3 hours later, her younger sister left their home and drove towards the same town at 100 km/h. When the younger sister reached the town at 6.55 p.m., Usha had another 6 km to travel. What was Usha’s average speed? Express your answer in mixed number.
Time that the Usha's younger sister started driving = 1.55 p.m.
Duration that Usha's younger sister drove from 1.55 p.m. to 6.55 p.m. = 5 h

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

Distance that Usha travelled by the time her younger sister reached the city
= 500 - 6
= 494 km

Time that Usha took to travel 494 km = 8 h

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

Answer(s): 61³₄ km/h