Mrs Yeo left home at 7 a.m. and drove towards the city. 3¹₃ hour later, Mr Yeo left the house and drove at an average speed of 108 km/h towards the city. When Mr Yeo reached his destination at 3 p.m., Mrs Yeo was 15 km away from the city. Find Mrs Yeo’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
¹₃ h = ¹₃ x 60 = 20 min
3¹₃ = 3 h 20 min

3 h 20 min after 7 a.m. = 10.20 a.m.

Time that Mr Yeo left the house = 10.20 a.m.

Time that Mr Yeo took from 10.20 a.m. to 3 p.m. to reach his destination = 4 h 40 min

1 min = ¹₆₀ h
40 min = ⁴⁰₆₀ h = ²₃ h
4 h 40 min = 4²₃ h

Distance that Mr Yeo drove
= 4²₃ x 108
= 504 km

Distance that Mrs Yeo drove when Mr Yeo reached
= 504 - 15 
= 489 km

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

Mrs Yeo's average speed
= 489 ÷ 8
= 61¹₈ km/h

Answer(s): 61¹₈ km/h