Mrs Chiam left home at 7 a.m. and drove towards the city. 3⁵₁₂ hour later, Mr Chiam left the house and drove at an average speed of 107 km/h towards the city. When Mr Chiam reached his destination at 2 p.m., Mrs Chiam was 11 km away from the city. Find Mrs Chiam’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
⁵₁₂ h = ⁵₁₂ x 60 = 25 min
3⁵₁₂ = 3 h 25 min

3 h 25 min after 7 a.m. = 10.25 a.m.

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

Time that Mr Chiam took from 10.25 a.m. to 2 p.m. to reach his destination = 3 h 35 min

1 min = ¹₆₀ h
35 min = ³⁵₆₀ h = ⁷₁₂ h
3 h 35 min = 3⁷₁₂ h

Distance that Mr Chiam drove
= 3⁷₁₂ x 107
= 383⁵₁₂ km

Distance that Mrs Chiam drove when Mr Chiam reached
= 383⁵₁₂ - 11 
= 372⁵₁₂ km

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

Mrs Chiam's average speed
= 372⁵₁₂ ÷ 7
= 53¹⁷₈₄ km/h

Answer(s): 53¹⁷₈₄ km/h