Diana left home at 11.40 a.m. and drove towards the city. 2 hours later, her cousin left their home and drove towards the same city at 86 km/h. When the cousin reached the city at 6.40 p.m., Diana had another 3 km to travel. What was Diana’s average speed? Express your answer in mixed number.
Time that the Diana's cousin started driving = 1.40 p.m.
Duration that Diana's cousin drove from 1.40 p.m. to 6.40 p.m. = 5 h

Distance that Diana's cousin travelled
= 5 x 86
= 430 km

Distance that Diana travelled by the time her cousin reached the city
= 430 - 3
= 427 km

Time that Diana took to travel 427 km = 7 h

Diana's average speed
= 427 ÷ 7
= 61 km/h

Answer(s): 61 km/h