Mrs Chau left home at 7 a.m. and drove towards the city. 1²₃ hour later, Mr Chau left the house and drove at an average speed of 88 km/h towards the city. When Mr Chau reached his destination at 1 p.m., Mrs Chau was 19 km away from the city. Find Mrs Chau’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
²₃ h = ²₃ x 60 = 40 min
1²₃ = 1 h 40 min

1 h 40 min after 7 a.m. = 8.40 a.m.

Time that Mr Chau left the house = 8.40 a.m.

Time that Mr Chau took from 8.40 a.m. to 1 p.m. to reach his destination = 4 h 20 min

1 min = ¹₆₀ h
20 min = ²⁰₆₀ h = ¹₃ h
4 h 20 min = 4¹₃ h

Distance that Mr Chau drove
= 4¹₃ x 88
= 381¹₃ km

Distance that Mrs Chau drove when Mr Chau reached
= 381¹₃ - 19 
= 362¹₃ km

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

Mrs Chau's average speed
= 362¹₃ ÷ 6
= 60⁷₁₈ km/h

Answer(s): 60⁷₁₈ km/h