Hilda left home at 11.40 a.m. and drove towards the seaside resort. 2 hours later, her younger brother left their home and drove towards the same seaside resort at 89 km/h. When the younger brother reached the seaside resort at 4.40 p.m., Hilda had another 4 km to travel. What was Hilda’s average speed? Express your answer in mixed number.
Time that the Hilda's younger brother started driving = 1.40 p.m.
Duration that Hilda's younger brother drove from 1.40 p.m. to 4.40 p.m. = 3 h

Distance that Hilda's younger brother travelled
= 3 x 89
= 267 km

Distance that Hilda travelled by the time her younger brother reached the city
= 267 - 4
= 263 km

Time that Hilda took to travel 263 km = 5 h

Hilda's average speed
= 263 ÷ 5
= 52³₅ km/h

Answer(s): 52³₅ km/h