Mrs Chia left home at 9 a.m. and drove towards the city. 1¹₄ hour later, Mr Chia left the house and drove at an average speed of 87 km/h towards the city. When Mr Chia reached his destination at 3 p.m., Mrs Chia was 19 km away from the city. Find Mrs Chia’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 9 a.m. = 10.15 a.m.

Time that Mr Chia left the house = 10.15 a.m.

Time that Mr Chia took from 10.15 a.m. to 3 p.m. to reach his destination = 4 h 45 min

1 min = ¹₆₀ h
45 min = ⁴⁵₆₀ h = ³₄ h
4 h 45 min = 4³₄ h

Distance that Mr Chia drove
= 4³₄ x 87
= 413¹₄ km

Distance that Mrs Chia drove when Mr Chia reached
= 413¹₄ - 19 
= 394¹₄ km

Time that Mrs Chia took to travel from 9 a.m. to 3 p.m. = 6 h

Mrs Chia's average speed
= 394¹₄ ÷ 6
= 65¹⁷₂₄ km/h

Answer(s): 65¹⁷₂₄ km/h