Mrs Yong left home at 7 a.m. and drove towards the city. 2¹₄ hour later, Mr Yong left the house and drove at an average speed of 85 km/h towards the city. When Mr Yong reached his destination at 2 p.m., Mrs Yong was 24 km away from the city. Find Mrs Yong’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
¹₄ h = ¹₄ x 60 = 15 min
2¹₄ = 2 h 15 min

2 h 15 min after 7 a.m. = 9.15 a.m.

Time that Mr Yong left the house = 9.15 a.m.

Time that Mr Yong took from 9.15 a.m. to 2 p.m. to reach his destination = 4 h 45 min

1 min = ¹₆₀ h
45 min = ⁴⁵₆₀ h = ³₄ h
4 h 45 min = 4³₄ h

Distance that Mr Yong drove
= 4³₄ x 85
= 403³₄ km

Distance that Mrs Yong drove when Mr Yong reached
= 403³₄ - 24 
= 379³₄ km

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

Mrs Yong's average speed
= 379³₄ ÷ 7
= 54¹₄ km/h

Answer(s): 54¹₄ km/h