Zara left home at 11.45 a.m. and drove towards the city. 3 hours later, her grandfather left their home and drove towards the same city at 99 km/h. When the grandfather reached the city at 6.45 p.m., Zara had another 4 km to travel. What was Zara’s average speed? Express your answer in mixed number.
Time that the Zara's grandfather started driving = 2.45 p.m.
Duration that Zara's grandfather drove from 2.45 p.m. to 6.45 p.m. = 4 h

Distance that Zara's grandfather travelled
= 4 x 99
= 396 km

Distance that Zara travelled by the time her grandfather reached the city
= 396 - 4
= 392 km

Time that Zara took to travel 392 km = 7 h

Zara's average speed
= 392 ÷ 7
= 56 km/h

Answer(s): 56 km/h