Yen left home at 11.50 a.m. and drove towards the seaside resort. 2 hours later, her uncle left their home and drove towards the same seaside resort at 75 km/h. When the uncle reached the seaside resort at 6.50 p.m., Yen had another 4 km to travel. What was Yen’s average speed? Express your answer in mixed number.
Time that the Yen's uncle started driving = 1.50 p.m.
Duration that Yen's uncle drove from 1.50 p.m. to 6.50 p.m. = 5 h

Distance that Yen's uncle travelled
= 5 x 75
= 375 km

Distance that Yen travelled by the time her uncle reached the city
= 375 - 4
= 371 km

Time that Yen took to travel 371 km = 7 h

Yen's average speed
= 371 ÷ 7
= 53 km/h

Answer(s): 53 km/h