Zara left home at 10.45 a.m. and drove towards the seaside resort. 3 hours later, her grandmother left their home and drove towards the same seaside resort at 90 km/h. When the grandmother reached the seaside resort 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 grandmother started driving = 1.45 p.m.
Duration that Zara's grandmother drove from 1.45 p.m. to 6.45 p.m. = 5 h

Distance that Zara's grandmother travelled
= 5 x 90
= 450 km

Distance that Zara travelled by the time her grandmother reached the city
= 450 - 4
= 446 km

Time that Zara took to travel 446 km = 8 h

Zara's average speed
= 446 ÷ 8
= 55³₄ km/h

Answer(s): 55³₄ km/h