Mrs Thia left home at 9 a.m. and drove towards the city. 2²₃ hour later, Mr Thia left the house and drove at an average speed of 106 km/h towards the city. When Mr Thia reached his destination at 3 p.m., Mrs Thia was 15 km away from the city. Find Mrs Thia’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
²₃ h = ²₃ x 60 = 40 min
2²₃ = 2 h 40 min

2 h 40 min after 9 a.m. = 11.40 a.m.

Time that Mr Thia left the house = 11.40 a.m.

Time that Mr Thia took from 11.40 a.m. to 3 p.m. to reach his destination = 3 h 20 min

1 min = ¹₆₀ h
20 min = ²⁰₆₀ h = ¹₃ h
3 h 20 min = 3¹₃ h

Distance that Mr Thia drove
= 3¹₃ x 106
= 353¹₃ km

Distance that Mrs Thia drove when Mr Thia reached
= 353¹₃ - 15 
= 338¹₃ km

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

Mrs Thia's average speed
= 338¹₃ ÷ 6
= 56⁷₁₈ km/h

Answer(s): 56⁷₁₈ km/h