Mrs Soh left home at 9 a.m. and drove towards the city. 2¹₃ hour later, Mr Soh left the house and drove at an average speed of 99 km/h towards the city. When Mr Soh reached his destination at 3 p.m., Mrs Soh was 10 km away from the city. Find Mrs Soh’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
¹₃ h = ¹₃ x 60 = 20 min
2¹₃ = 2 h 20 min

2 h 20 min after 9 a.m. = 11.20 a.m.

Time that Mr Soh left the house = 11.20 a.m.

Time that Mr Soh took from 11.20 a.m. to 3 p.m. to reach his destination = 3 h 40 min

1 min = ¹₆₀ h
40 min = ⁴⁰₆₀ h = ²₃ h
3 h 40 min = 3²₃ h

Distance that Mr Soh drove
= 3²₃ x 99
= 363 km

Distance that Mrs Soh drove when Mr Soh reached
= 363 - 10 
= 353 km

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

Mrs Soh's average speed
= 353 ÷ 6
= 58⁵₆ km/h

Answer(s): 58⁵₆ km/h