Mrs Ong left home at 7 a.m. and drove towards the city. 2³₄ hour later, Mr Ong left the house and drove at an average speed of 89 km/h towards the city. When Mr Ong reached his destination at 3 p.m., Mrs Ong was 23 km away from the city. Find Mrs Ong’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
³₄ h = ³₄ x 60 = 45 min
2³₄ = 2 h 45 min

2 h 45 min after 7 a.m. = 9.45 a.m.

Time that Mr Ong left the house = 9.45 a.m.

Time that Mr Ong took from 9.45 a.m. to 3 p.m. to reach his destination = 5 h 15 min

1 min = ¹₆₀ h
15 min = ¹⁵₆₀ h = ¹₄ h
5 h 15 min = 5¹₄ h

Distance that Mr Ong drove
= 5¹₄ x 89
= 467¹₄ km

Distance that Mrs Ong drove when Mr Ong reached
= 467¹₄ - 23 
= 444¹₄ km

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

Mrs Ong's average speed
= 444¹₄ ÷ 8
= 55¹⁷₃₂ km/h

Answer(s): 55¹⁷₃₂ km/h