Mrs Yong left home at 7 a.m. and drove towards the city. 2²₃ hour later, Mr Yong left the house and drove at an average speed of 107 km/h towards the city. When Mr Yong reached his destination at 1 p.m., Mrs Yong was 12 km away from the city. Find Mrs Yong’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 7 a.m. = 9.40 a.m.

Time that Mr Yong left the house = 9.40 a.m.

Time that Mr Yong took from 9.40 a.m. to 1 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 Yong drove
= 3¹₃ x 107
= 356²₃ km

Distance that Mrs Yong drove when Mr Yong reached
= 356²₃ - 12 
= 344²₃ km

Time that Mrs Yong took to travel from 7 a.m. to 1 p.m. = 6 h

Mrs Yong's average speed
= 344²₃ ÷ 6
= 57⁴₉ km/h

Answer(s): 57⁴₉ km/h