Mrs Toh left home at 9 a.m. and drove towards the city. 1³₄ hour later, Mr Toh left the house and drove at an average speed of 80 km/h towards the city. When Mr Toh reached his destination at 3 p.m., Mrs Toh was 13 km away from the city. Find Mrs Toh’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
³₄ h = ³₄ x 60 = 45 min
1³₄ = 1 h 45 min

1 h 45 min after 9 a.m. = 10.45 a.m.

Time that Mr Toh left the house = 10.45 a.m.

Time that Mr Toh took from 10.45 a.m. to 3 p.m. to reach his destination = 4 h 15 min

1 min = ¹₆₀ h
15 min = ¹⁵₆₀ h = ¹₄ h
4 h 15 min = 4¹₄ h

Distance that Mr Toh drove
= 4¹₄ x 80
= 340 km

Distance that Mrs Toh drove when Mr Toh reached
= 340 - 13 
= 327 km

Time that Mrs Toh took to travel from 9 a.m. to 3 p.m. = 6 h

Mrs Toh's average speed
= 327 ÷ 6
= 54¹₂ km/h

Answer(s): 54¹₂ km/h