Mrs Loh left home at 8 a.m. and drove towards the city. 1¹₃ hour later, Mr Loh left the house and drove at an average speed of 107 km/h towards the city. When Mr Loh reached his destination at 3 p.m., Mrs Loh was 21 km away from the city. Find Mrs Loh’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 8 a.m. = 9.20 a.m.

Time that Mr Loh left the house = 9.20 a.m.

Time that Mr Loh took from 9.20 a.m. to 3 p.m. to reach his destination = 5 h 40 min

1 min = ¹₆₀ h
40 min = ⁴⁰₆₀ h = ²₃ h
5 h 40 min = 5²₃ h

Distance that Mr Loh drove
= 5²₃ x 107
= 606¹₃ km

Distance that Mrs Loh drove when Mr Loh reached
= 606¹₃ - 21 
= 585¹₃ km

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

Mrs Loh's average speed
= 585¹₃ ÷ 7
= 83¹³₂₁ km/h

Answer(s): 83¹³₂₁ km/h