Mrs Kok left home at 9 a.m. and drove towards the city. 1¹₂ hour later, Mr Kok left the house and drove at an average speed of 82 km/h towards the city. When Mr Kok reached his destination at 3 p.m., Mrs Kok was 24 km away from the city. Find Mrs Kok’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
¹₂ h = ¹₂ x 60 = 30 min
1¹₂ = 1 h 30 min

1 h 30 min after 9 a.m. = 10.30 a.m.

Time that Mr Kok left the house = 10.30 a.m.

Time that Mr Kok took from 10.30 a.m. to 3 p.m. to reach his destination = 4 h 30 min

1 min = ¹₆₀ h
30 min = ³⁰₆₀ h = ¹₂ h
4 h 30 min = 4¹₂ h

Distance that Mr Kok drove
= 4¹₂ x 82
= 369 km

Distance that Mrs Kok drove when Mr Kok reached
= 369 - 24 
= 345 km

Time that Mrs Kok took to travel from 9 a.m. to 3 p.m. = 6 h

Mrs Kok's average speed
= 345 ÷ 6
= 57¹₂ km/h

Answer(s): 57¹₂ km/h