Mrs Lee left home at 7 a.m. and drove towards the city. 1²₃ hour later, Mr Lee left the house and drove at an average speed of 95 km/h towards the city. When Mr Lee reached his destination at 2 p.m., Mrs Lee was 18 km away from the city. Find Mrs Lee’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 7 a.m. = 8.40 a.m.

Time that Mr Lee left the house = 8.40 a.m.

Time that Mr Lee took from 8.40 a.m. to 2 p.m. to reach his destination = 5 h 20 min

1 min = ¹₆₀ h
20 min = ²⁰₆₀ h = ¹₃ h
5 h 20 min = 5¹₃ h

Distance that Mr Lee drove
= 5¹₃ x 95
= 506²₃ km

Distance that Mrs Lee drove when Mr Lee reached
= 506²₃ - 18 
= 488²₃ km

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

Mrs Lee's average speed
= 488²₃ ÷ 7
= 69¹⁷₂₁ km/h

Answer(s): 69¹⁷₂₁ km/h