Mrs Lu left home at 9 a.m. and drove towards the city. 1³₄ hour later, Mr Lu left the house and drove at an average speed of 96 km/h towards the city. When Mr Lu reached his destination at 2 p.m., Mrs Lu was 23 km away from the city. Find Mrs Lu’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
³₄ h = ³₄ x 60 = 45 min
1³₄ = 1 h 45 min

1 h 45 min after 9 a.m. = 10.45 a.m.

Time that Mr Lu left the house = 10.45 a.m.

Time that Mr Lu took from 10.45 a.m. to 2 p.m. to reach his destination = 3 h 15 min

1 min = ¹₆₀ h
15 min = ¹⁵₆₀ h = ¹₄ h
3 h 15 min = 3¹₄ h

Distance that Mr Lu drove
= 3¹₄ x 96
= 312 km

Distance that Mrs Lu drove when Mr Lu reached
= 312 - 23 
= 289 km

Time that Mrs Lu took to travel from 9 a.m. to 2 p.m. = 5 h

Mrs Lu's average speed
= 289 ÷ 5
= 57⁴₅ km/h

Answer(s): 57⁴₅ km/h