Eva left home at 11.15 a.m. and drove towards the campsite. 2 hours later, her younger sister left their home and drove towards the same campsite at 87 km/h. When the younger sister reached the campsite at 4.15 p.m., Eva had another 6 km to travel. What was Eva’s average speed? Express your answer in mixed number.
Time that the Eva's younger sister started driving = 1.15 p.m.
Duration that Eva's younger sister drove from 1.15 p.m. to 4.15 p.m. = 3 h

Distance that Eva's younger sister travelled
= 3 x 87
= 261 km

Distance that Eva travelled by the time her younger sister reached the city
= 261 - 6
= 255 km

Time that Eva took to travel 255 km = 5 h

Eva's average speed
= 255 ÷ 5
= 51 km/h

Answer(s): 51 km/h