Mrs Koh left home at 10 a.m. and drove towards the city. 1¹₄ hour later, Mr Koh left the house and drove at an average speed of 107 km/h towards the city. When Mr Koh reached his destination at 2 p.m., Mrs Koh was 25 km away from the city. Find Mrs Koh’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
¹₄ h = ¹₄ x 60 = 15 min
1¹₄ = 1 h 15 min

1 h 15 min after 10 a.m. = 11.15 a.m.

Time that Mr Koh left the house = 11.15 a.m.

Time that Mr Koh took from 11.15 a.m. to 2 p.m. to reach his destination = 2 h 45 min

1 min = ¹₆₀ h
45 min = ⁴⁵₆₀ h = ³₄ h
2 h 45 min = 2³₄ h

Distance that Mr Koh drove
= 2³₄ x 107
= 294¹₄ km

Distance that Mrs Koh drove when Mr Koh reached
= 294¹₄ - 25 
= 269¹₄ km

Time that Mrs Koh took to travel from 10 a.m. to 2 p.m. = 4 h

Mrs Koh's average speed
= 269¹₄ ÷ 4
= 67⁵₁₆ km/h

Answer(s): 67⁵₁₆ km/h