Mrs Chia left home at 7 a.m. and drove towards the city. 1¹₃ hour later, Mr Chia left the house and drove at an average speed of 91 km/h towards the city. When Mr Chia reached his destination at 2 p.m., Mrs Chia was 22 km away from the city. Find Mrs Chia’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 Chia left the house = 8.20 a.m.

Time that Mr Chia took from 8.20 a.m. to 2 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 Chia drove
= 5²₃ x 91
= 515²₃ km

Distance that Mrs Chia drove when Mr Chia reached
= 515²₃ - 22 
= 493²₃ km

Time that Mrs Chia took to travel from 7 a.m. to 2 p.m. = 7 h

Mrs Chia's average speed
= 493²₃ ÷ 7
= 70¹¹₂₁ km/h

Answer(s): 70¹¹₂₁ km/h