Mrs Koh left home at 7 a.m. and drove towards the city. 2¹₄ hour later, Mr Koh left the house and drove at an average speed of 87 km/h towards the city. When Mr Koh reached his destination at 3 p.m., Mrs Koh was 22 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
2¹₄ = 2 h 15 min

2 h 15 min after 7 a.m. = 9.15 a.m.

Time that Mr Koh left the house = 9.15 a.m.

Time that Mr Koh took from 9.15 a.m. to 3 p.m. to reach his destination = 5 h 45 min

1 min = ¹₆₀ h
45 min = ⁴⁵₆₀ h = ³₄ h
5 h 45 min = 5³₄ h

Distance that Mr Koh drove
= 5³₄ x 87
= 500¹₄ km

Distance that Mrs Koh drove when Mr Koh reached
= 500¹₄ - 22 
= 478¹₄ km

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

Mrs Koh's average speed
= 478¹₄ ÷ 8
= 59²⁵₃₂ km/h

Answer(s): 59²⁵₃₂ km/h