Erika left home at 11.50 a.m. and drove towards the countryside. 3 hours later, her mother left their home and drove towards the same countryside at 86 km/h. When the mother reached the countryside at 7.50 p.m., Erika had another 6 km to travel. What was Erika’s average speed? Express your answer in mixed number.
Time that the Erika's mother started driving = 2.50 p.m.
Duration that Erika's mother drove from 2.50 p.m. to 7.50 p.m. = 5 h

Distance that Erika's mother travelled
= 5 x 86
= 430 km

Distance that Erika travelled by the time her mother reached the city
= 430 - 6
= 424 km

Time that Erika took to travel 424 km = 8 h

Erika's average speed
= 424 ÷ 8
= 53 km/h

Answer(s): 53 km/h