Cathy left home at 11.20 a.m. and drove towards the countryside. 2 hours later, her younger sister left their home and drove towards the same countryside at 96 km/h. When the younger sister reached the countryside at 4.20 p.m., Cathy had another 3 km to travel. What was Cathy’s average speed? Express your answer in mixed number.
Time that the Cathy's younger sister started driving = 1.20 p.m.
Duration that Cathy's younger sister drove from 1.20 p.m. to 4.20 p.m. = 3 h

Distance that Cathy's younger sister travelled
= 3 x 96
= 288 km

Distance that Cathy travelled by the time her younger sister reached the city
= 288 - 3
= 285 km

Time that Cathy took to travel 285 km = 5 h

Cathy's average speed
= 285 ÷ 5
= 57 km/h

Answer(s): 57 km/h