Rachel left home at 11.35 a.m. and drove towards the town. 2 hours later, her younger sister left their home and drove towards the same town at 93 km/h. When the younger sister reached the town at 4.35 p.m., Rachel had another 4 km to travel. What was Rachel’s average speed? Express your answer in mixed number.
Time that the Rachel's younger sister started driving = 1.35 p.m.
Duration that Rachel's younger sister drove from 1.35 p.m. to 4.35 p.m. = 3 h

Distance that Rachel's younger sister travelled
= 3 x 93
= 279 km

Distance that Rachel travelled by the time her younger sister reached the city
= 279 - 4
= 275 km

Time that Rachel took to travel 275 km = 5 h

Rachel's average speed
= 275 ÷ 5
= 55 km/h

Answer(s): 55 km/h