Mrs Yee left home at 8 a.m. and drove towards the city. 1²₃ hour later, Mr Yee left the house and drove at an average speed of 84 km/h towards the city. When Mr Yee reached his destination at 1 p.m., Mrs Yee was 22 km away from the city. Find Mrs Yee’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 8 a.m. = 9.40 a.m.

Time that Mr Yee left the house = 9.40 a.m.

Time that Mr Yee took from 9.40 a.m. to 1 p.m. to reach his destination = 3 h 20 min

1 min = ¹₆₀ h
20 min = ²⁰₆₀ h = ¹₃ h
3 h 20 min = 3¹₃ h

Distance that Mr Yee drove
= 3¹₃ x 84
= 280 km

Distance that Mrs Yee drove when Mr Yee reached
= 280 - 22 
= 258 km

Time that Mrs Yee took to travel from 8 a.m. to 1 p.m. = 5 h

Mrs Yee's average speed
= 258 ÷ 5
= 51³₅ km/h

Answer(s): 51³₅ km/h