Mrs Chen left home at 7 a.m. and drove towards the city. 1¹₂ hour later, Mr Chen left the house and drove at an average speed of 84 km/h towards the city. When Mr Chen reached his destination at 2 p.m., Mrs Chen was 27 km away from the city. Find Mrs Chen’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
¹₂ h = ¹₂ x 60 = 30 min
1¹₂ = 1 h 30 min

1 h 30 min after 7 a.m. = 8.30 a.m.

Time that Mr Chen left the house = 8.30 a.m.

Time that Mr Chen took from 8.30 a.m. to 2 p.m. to reach his destination = 5 h 30 min

1 min = ¹₆₀ h
30 min = ³⁰₆₀ h = ¹₂ h
5 h 30 min = 5¹₂ h

Distance that Mr Chen drove
= 5¹₂ x 84
= 462 km

Distance that Mrs Chen drove when Mr Chen reached
= 462 - 27 
= 435 km

Time that Mrs Chen took to travel from 7 a.m. to 2 p.m. = 7 h

Mrs Chen's average speed
= 435 ÷ 7
= 62¹₇ km/h

Answer(s): 62¹₇ km/h