Mrs Chan left home at 8 a.m. and drove towards the city. 1¹₃ hour later, Mr Chan left the house and drove at an average speed of 106 km/h towards the city. When Mr Chan reached his destination at 2 p.m., Mrs Chan was 25 km away from the city. Find Mrs Chan’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 8 a.m. = 9.20 a.m.

Time that Mr Chan left the house = 9.20 a.m.

Time that Mr Chan took from 9.20 a.m. to 2 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 Chan drove
= 4²₃ x 106
= 494²₃ km

Distance that Mrs Chan drove when Mr Chan reached
= 494²₃ - 25 
= 469²₃ km

Time that Mrs Chan took to travel from 8 a.m. to 2 p.m. = 6 h

Mrs Chan's average speed
= 469²₃ ÷ 6
= 78⁵₁₈ km/h

Answer(s): 78⁵₁₈ km/h