Mrs Heng left home at 7 a.m. and drove towards the city. 2¹₂ hour later, Mr Heng left the house and drove at an average speed of 98 km/h towards the city. When Mr Heng reached his destination at 2 p.m., Mrs Heng was 19 km away from the city. Find Mrs Heng’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
¹₂ h = ¹₂ x 60 = 30 min
2¹₂ = 2 h 30 min

2 h 30 min after 7 a.m. = 9.30 a.m.

Time that Mr Heng left the house = 9.30 a.m.

Time that Mr Heng took from 9.30 a.m. to 2 p.m. to reach his destination = 4 h 30 min

1 min = ¹₆₀ h
30 min = ³⁰₆₀ h = ¹₂ h
4 h 30 min = 4¹₂ h

Distance that Mr Heng drove
= 4¹₂ x 98
= 441 km

Distance that Mrs Heng drove when Mr Heng reached
= 441 - 19 
= 422 km

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

Mrs Heng's average speed
= 422 ÷ 7
= 60²₇ km/h

Answer(s): 60²₇ km/h