Natalie left home at 11.55 a.m. and drove towards the countryside. 3 hours later, her cousin left their home and drove towards the same countryside at 100 km/h. When the cousin reached the countryside at 7.55 p.m., Natalie had another 4 km to travel. What was Natalie’s average speed? Express your answer in mixed number.
Time that the Natalie's cousin started driving = 2.55 p.m.
Duration that Natalie's cousin drove from 2.55 p.m. to 7.55 p.m. = 5 h

Distance that Natalie's cousin travelled
= 5 x 100
= 500 km

Distance that Natalie travelled by the time her cousin reached the city
= 500 - 4
= 496 km

Time that Natalie took to travel 496 km = 8 h

Natalie's average speed
= 496 ÷ 8
= 62 km/h

Answer(s): 62 km/h