Mrs Zhang left home at 9 a.m. and drove towards the city. 2³₄ hour later, Mr Zhang left the house and drove at an average speed of 101 km/h towards the city. When Mr Zhang reached his destination at 3 p.m., Mrs Zhang was 15 km away from the city. Find Mrs Zhang’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 9 a.m. = 11.45 a.m.

Time that Mr Zhang left the house = 11.45 a.m.

Time that Mr Zhang took from 11.45 a.m. to 3 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 Zhang drove
= 3¹₄ x 101
= 328¹₄ km

Distance that Mrs Zhang drove when Mr Zhang reached
= 328¹₄ - 15 
= 313¹₄ km

Time that Mrs Zhang took to travel from 9 a.m. to 3 p.m. = 6 h

Mrs Zhang's average speed
= 313¹₄ ÷ 6
= 52⁵₂₄ km/h

Answer(s): 52⁵₂₄ km/h