Mrs Pang left home at 7 a.m. and drove towards the city. 2⁷₁₂ hour later, Mr Pang left the house and drove at an average speed of 101 km/h towards the city. When Mr Pang reached his destination at 1 p.m., Mrs Pang was 18 km away from the city. Find Mrs Pang’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
⁷₁₂ h = ⁷₁₂ x 60 = 35 min
2⁷₁₂ = 2 h 35 min

2 h 35 min after 7 a.m. = 9.35 a.m.

Time that Mr Pang left the house = 9.35 a.m.

Time that Mr Pang took from 9.35 a.m. to 1 p.m. to reach his destination = 3 h 25 min

1 min = ¹₆₀ h
25 min = ²⁵₆₀ h = ⁵₁₂ h
3 h 25 min = 3⁵₁₂ h

Distance that Mr Pang drove
= 3⁵₁₂ x 101
= 345¹₁₂ km

Distance that Mrs Pang drove when Mr Pang reached
= 345¹₁₂ - 18 
= 327¹₁₂ km

Time that Mrs Pang took to travel from 7 a.m. to 1 p.m. = 6 h

Mrs Pang's average speed
= 327¹₁₂ ÷ 6
= 54³⁷₇₂ km/h

Answer(s): 54³⁷₇₂ km/h