Mrs Soh left home at 7 a.m. and drove towards the city. 2⁷₁₂ hour later, Mr Soh left the house and drove at an average speed of 107 km/h towards the city. When Mr Soh reached his destination at 2 p.m., Mrs Soh was 16 km away from the city. Find Mrs Soh’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
⁷₁₂ h = ⁷₁₂ x 60 = 35 min
2⁷₁₂ = 2 h 35 min

2 h 35 min after 7 a.m. = 9.35 a.m.

Time that Mr Soh left the house = 9.35 a.m.

Time that Mr Soh took from 9.35 a.m. to 2 p.m. to reach his destination = 4 h 25 min

1 min = ¹₆₀ h
25 min = ²⁵₆₀ h = ⁵₁₂ h
4 h 25 min = 4⁵₁₂ h

Distance that Mr Soh drove
= 4⁵₁₂ x 107
= 472⁷₁₂ km

Distance that Mrs Soh drove when Mr Soh reached
= 472⁷₁₂ - 16 
= 456⁷₁₂ km

Time that Mrs Soh took to travel from 7 a.m. to 2 p.m. = 7 h

Mrs Soh's average speed
= 456⁷₁₂ ÷ 7
= 65¹⁹₈₄ km/h

Answer(s): 65¹⁹₈₄ km/h