Mrs Lin left home at 8 a.m. and drove towards the city. 1¹₂ hour later, Mr Lin left the house and drove at an average speed of 105 km/h towards the city. When Mr Lin reached his destination at 3 p.m., Mrs Lin was 14 km away from the city. Find Mrs Lin’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 8 a.m. = 9.30 a.m.

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

Time that Mr Lin took from 9.30 a.m. to 3 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 Lin drove
= 5¹₂ x 105
= 577¹₂ km

Distance that Mrs Lin drove when Mr Lin reached
= 577¹₂ - 14 
= 563¹₂ km

Time that Mrs Lin took to travel from 8 a.m. to 3 p.m. = 7 h

Mrs Lin's average speed
= 563¹₂ ÷ 7
= 80¹₂ km/h

Answer(s): 80¹₂ km/h