Mrs Sim left home at 10 a.m. and drove towards the city. 1¹₃ hour later, Mr Sim left the house and drove at an average speed of 91 km/h towards the city. When Mr Sim reached his destination at 3 p.m., Mrs Sim was 19 km away from the city. Find Mrs Sim’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
¹₃ h = ¹₃ x 60 = 20 min
1¹₃ = 1 h 20 min

1 h 20 min after 10 a.m. = 11.20 a.m.

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

Time that Mr Sim 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 Sim drove
= 3²₃ x 91
= 333²₃ km

Distance that Mrs Sim drove when Mr Sim reached
= 333²₃ - 19 
= 314²₃ km

Time that Mrs Sim took to travel from 10 a.m. to 3 p.m. = 5 h

Mrs Sim's average speed
= 314²₃ ÷ 5
= 62¹⁴₁₅ km/h

Answer(s): 62¹⁴₁₅ km/h