Mrs Lau left home at 8 a.m. and drove towards the city. 2⁵₁₂ hour later, Mr Lau left the house and drove at an average speed of 97 km/h towards the city. When Mr Lau reached his destination at 3 p.m., Mrs Lau was 26 km away from the city. Find Mrs Lau’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
⁵₁₂ h = ⁵₁₂ x 60 = 25 min
2⁵₁₂ = 2 h 25 min

2 h 25 min after 8 a.m. = 10.25 a.m.

Time that Mr Lau left the house = 10.25 a.m.

Time that Mr Lau took from 10.25 a.m. to 3 p.m. to reach his destination = 4 h 35 min

1 min = ¹₆₀ h
35 min = ³⁵₆₀ h = ⁷₁₂ h
4 h 35 min = 4⁷₁₂ h

Distance that Mr Lau drove
= 4⁷₁₂ x 97
= 444⁷₁₂ km

Distance that Mrs Lau drove when Mr Lau reached
= 444⁷₁₂ - 26 
= 418⁷₁₂ km

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

Mrs Lau's average speed
= 418⁷₁₂ ÷ 7
= 59⁶⁷₈₄ km/h

Answer(s): 59⁶⁷₈₄ km/h