Mrs Sim left home at 8 a.m. and drove towards the city. 1¹₂ hour later, Mr Sim left the house and drove at an average speed of 103 km/h towards the city. When Mr Sim reached his destination at 2 p.m., Mrs Sim was 13 km away from the city. Find Mrs Sim’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 Sim left the house = 9.30 a.m.

Time that Mr Sim 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 Sim drove
= 4¹₂ x 103
= 463¹₂ km

Distance that Mrs Sim drove when Mr Sim reached
= 463¹₂ - 13 
= 450¹₂ km

Time that Mrs Sim took to travel from 8 a.m. to 2 p.m. = 6 h

Mrs Sim's average speed
= 450¹₂ ÷ 6
= 75¹₁₂ km/h

Answer(s): 75¹₁₂ km/h