Mrs Lim left home at 7 a.m. and drove towards the city. 2¹₂ hour later, Mr Lim left the house and drove at an average speed of 108 km/h towards the city. When Mr Lim reached his destination at 2 p.m., Mrs Lim was 29 km away from the city. Find Mrs Lim’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
¹₂ h = ¹₂ x 60 = 30 min
2¹₂ = 2 h 30 min

2 h 30 min after 7 a.m. = 9.30 a.m.

Time that Mr Lim left the house = 9.30 a.m.

Time that Mr Lim took from 9.30 a.m. to 2 p.m. to reach his destination = 4 h 30 min

1 min = ¹₆₀ h
30 min = ³⁰₆₀ h = ¹₂ h
4 h 30 min = 4¹₂ h

Distance that Mr Lim drove
= 4¹₂ x 108
= 486 km

Distance that Mrs Lim drove when Mr Lim reached
= 486 - 29 
= 457 km

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

Mrs Lim's average speed
= 457 ÷ 7
= 65²₇ km/h

Answer(s): 65²₇ km/h