Mrs Lu left home at 7 a.m. and drove towards the city. 2¹₄ hour later, Mr Lu left the house and drove at an average speed of 97 km/h towards the city. When Mr Lu reached his destination at 3 p.m., Mrs Lu was 12 km away from the city. Find Mrs Lu’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
¹₄ h = ¹₄ x 60 = 15 min
2¹₄ = 2 h 15 min

2 h 15 min after 7 a.m. = 9.15 a.m.

Time that Mr Lu left the house = 9.15 a.m.

Time that Mr Lu took from 9.15 a.m. to 3 p.m. to reach his destination = 5 h 45 min

1 min = ¹₆₀ h
45 min = ⁴⁵₆₀ h = ³₄ h
5 h 45 min = 5³₄ h

Distance that Mr Lu drove
= 5³₄ x 97
= 557³₄ km

Distance that Mrs Lu drove when Mr Lu reached
= 557³₄ - 12 
= 545³₄ km

Time that Mrs Lu took to travel from 7 a.m. to 3 p.m. = 8 h

Mrs Lu's average speed
= 545³₄ ÷ 8
= 68⁷₃₂ km/h

Answer(s): 68⁷₃₂ km/h