Mrs Seah left home at 10 a.m. and drove towards the city. 1⁵₁₂ hour later, Mr Seah left the house and drove at an average speed of 107 km/h towards the city. When Mr Seah reached his destination at 1 p.m., Mrs Seah was 15 km away from the city. Find Mrs Seah’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
⁵₁₂ h = ⁵₁₂ x 60 = 25 min
1⁵₁₂ = 1 h 25 min

1 h 25 min after 10 a.m. = 11.25 a.m.

Time that Mr Seah left the house = 11.25 a.m.

Time that Mr Seah took from 11.25 a.m. to 1 p.m. to reach his destination = 1 h 35 min

1 min = ¹₆₀ h
35 min = ³⁵₆₀ h = ⁷₁₂ h
1 h 35 min = 1⁷₁₂ h

Distance that Mr Seah drove
= 1⁷₁₂ x 107
= 169⁵₁₂ km

Distance that Mrs Seah drove when Mr Seah reached
= 169⁵₁₂ - 15 
= 154⁵₁₂ km

Time that Mrs Seah took to travel from 10 a.m. to 1 p.m. = 3 h

Mrs Seah's average speed
= 154⁵₁₂ ÷ 3
= 51¹⁷₃₆ km/h

Answer(s): 51¹⁷₃₆ km/h