Mrs Lu left home at 7 a.m. and drove towards the city. 2³₄ hour later, Mr Lu left the house and drove at an average speed of 104 km/h towards the city. When Mr Lu reached his destination at 2 p.m., Mrs Lu was 30 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
2³₄ = 2 h 45 min

2 h 45 min after 7 a.m. = 9.45 a.m.

Time that Mr Lu left the house = 9.45 a.m.

Time that Mr Lu took from 9.45 a.m. to 2 p.m. to reach his destination = 4 h 15 min

1 min = ¹₆₀ h
15 min = ¹⁵₆₀ h = ¹₄ h
4 h 15 min = 4¹₄ h

Distance that Mr Lu drove
= 4¹₄ x 104
= 442 km

Distance that Mrs Lu drove when Mr Lu reached
= 442 - 30 
= 412 km

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

Mrs Lu's average speed
= 412 ÷ 7
= 58⁶₇ km/h

Answer(s): 58⁶₇ km/h