Xylia left home at 11.40 a.m. and drove towards the seaside resort. 2 hours later, her auntie left their home and drove towards the same seaside resort at 78 km/h. When the auntie reached the seaside resort at 5.40 p.m., Xylia had another 3 km to travel. What was Xylia’s average speed? Express your answer in mixed number.
Time that the Xylia's auntie started driving = 1.40 p.m.
Duration that Xylia's auntie drove from 1.40 p.m. to 5.40 p.m. = 4 h

Distance that Xylia's auntie travelled
= 4 x 78
= 312 km

Distance that Xylia travelled by the time her auntie reached the city
= 312 - 3
= 309 km

Time that Xylia took to travel 309 km = 6 h

Xylia's average speed
= 309 ÷ 6
= 51¹₂ km/h

Answer(s): 51¹₂ km/h