Esther left home at 11.30 a.m. and drove towards the suburb. 2 hours later, her grandmother left their home and drove towards the same suburb at 90 km/h. When the grandmother reached the suburb at 5.30 p.m., Esther had another 3 km to travel. What was Esther’s average speed? Express your answer in mixed number.
Time that the Esther's grandmother started driving = 1.30 p.m.
Duration that Esther's grandmother drove from 1.30 p.m. to 5.30 p.m. = 4 h

Distance that Esther's grandmother travelled
= 4 x 90
= 360 km

Distance that Esther travelled by the time her grandmother reached the city
= 360 - 3
= 357 km

Time that Esther took to travel 357 km = 6 h

Esther's average speed
= 357 ÷ 6
= 59¹₂ km/h

Answer(s): 59¹₂ km/h