Erika left home at 11.30 a.m. and drove towards the campsite. 3 hours later, her younger brother left their home and drove towards the same campsite at 87 km/h. When the younger brother reached the campsite at 7.30 p.m., Erika had another 5 km to travel. What was Erika’s average speed? Express your answer in mixed number.
Time that the Erika's younger brother started driving = 2.30 p.m.
Duration that Erika's younger brother drove from 2.30 p.m. to 7.30 p.m. = 5 h

Distance that Erika's younger brother travelled
= 5 x 87
= 435 km

Distance that Erika travelled by the time her younger brother reached the city
= 435 - 5
= 430 km

Time that Erika took to travel 430 km = 8 h

Erika's average speed
= 430 ÷ 8
= 53³₄ km/h

Answer(s): 53³₄ km/h