Mrs Chew left home at 7 a.m. and drove towards the city. 1¹₃ hour later, Mr Chew left the house and drove at an average speed of 104 km/h towards the city. When Mr Chew reached his destination at 3 p.m., Mrs Chew was 27 km away from the city. Find Mrs Chew’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
¹₃ h = ¹₃ x 60 = 20 min
1¹₃ = 1 h 20 min

1 h 20 min after 7 a.m. = 8.20 a.m.

Time that Mr Chew left the house = 8.20 a.m.

Time that Mr Chew took from 8.20 a.m. to 3 p.m. to reach his destination = 6 h 40 min

1 min = ¹₆₀ h
40 min = ⁴⁰₆₀ h = ²₃ h
6 h 40 min = 6²₃ h

Distance that Mr Chew drove
= 6²₃ x 104
= 693¹₃ km

Distance that Mrs Chew drove when Mr Chew reached
= 693¹₃ - 27 
= 666¹₃ km

Time that Mrs Chew took to travel from 7 a.m. to 3 p.m. = 8 h

Mrs Chew's average speed
= 666¹₃ ÷ 8
= 83⁷₂₄ km/h

Answer(s): 83⁷₂₄ km/h