Natalie left home at 11.45 a.m. and drove towards the city. 2 hours later, her grandmother left their home and drove towards the same city at 76 km/h. When the grandmother reached the city at 6.45 p.m., Natalie had another 2 km to travel. What was Natalie’s average speed? Express your answer in mixed number.
Time that the Natalie's grandmother started driving = 1.45 p.m.
Duration that Natalie's grandmother drove from 1.45 p.m. to 6.45 p.m. = 5 h

Distance that Natalie's grandmother travelled
= 5 x 76
= 380 km

Distance that Natalie travelled by the time her grandmother reached the city
= 380 - 2
= 378 km

Time that Natalie took to travel 378 km = 7 h

Natalie's average speed
= 378 ÷ 7
= 54 km/h

Answer(s): 54 km/h