Mrs Toh left home at 8 a.m. and drove towards the city. 1¹₂ hour later, Mr Toh left the house and drove at an average speed of 104 km/h towards the city. When Mr Toh reached his destination at 2 p.m., Mrs Toh was 25 km away from the city. Find Mrs Toh’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 Toh left the house = 9.30 a.m.

Time that Mr Toh 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 Toh drove
= 4¹₂ x 104
= 468 km

Distance that Mrs Toh drove when Mr Toh reached
= 468 - 25 
= 443 km

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

Mrs Toh's average speed
= 443 ÷ 6
= 73⁵₆ km/h

Answer(s): 73⁵₆ km/h