Mrs Lu left home at 8 a.m. and drove towards the city. 1¹₃ hour later, Mr Lu left the house and drove at an average speed of 82 km/h towards the city. When Mr Lu reached his destination at 2 p.m., Mrs Lu was 28 km away from the city. Find Mrs Lu’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 Lu left the house = 9.20 a.m.

Time that Mr Lu 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 Lu drove
= 4²₃ x 82
= 382²₃ km

Distance that Mrs Lu drove when Mr Lu reached
= 382²₃ - 28 
= 354²₃ km

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

Mrs Lu's average speed
= 354²₃ ÷ 6
= 59¹₉ km/h

Answer(s): 59¹₉ km/h