Mrs Ma left home at 7 a.m. and drove towards the city. 1²₃ hour later, Mr Ma left the house and drove at an average speed of 107 km/h towards the city. When Mr Ma reached his destination at 1 p.m., Mrs Ma was 26 km away from the city. Find Mrs Ma’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 Ma left the house = 8.40 a.m.

Time that Mr Ma took from 8.40 a.m. to 1 p.m. to reach his destination = 4 h 20 min

1 min = ¹₆₀ h
20 min = ²⁰₆₀ h = ¹₃ h
4 h 20 min = 4¹₃ h

Distance that Mr Ma drove
= 4¹₃ x 107
= 463²₃ km

Distance that Mrs Ma drove when Mr Ma reached
= 463²₃ - 26 
= 437²₃ km

Time that Mrs Ma took to travel from 7 a.m. to 1 p.m. = 6 h

Mrs Ma's average speed
= 437²₃ ÷ 6
= 72¹⁷₁₈ km/h

Answer(s): 72¹⁷₁₈ km/h