Mrs Fong left home at 10 a.m. and drove towards the city. 1¹₆ hour later, Mr Fong left the house and drove at an average speed of 90 km/h towards the city. When Mr Fong reached his destination at 3 p.m., Mrs Fong was 14 km away from the city. Find Mrs Fong’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
¹₆ h = ¹₆ x 60 = 10 min
1¹₆ = 1 h 10 min

1 h 10 min after 10 a.m. = 11.10 a.m.

Time that Mr Fong left the house = 11.10 a.m.

Time that Mr Fong took from 11.10 a.m. to 3 p.m. to reach his destination = 3 h 50 min

1 min = ¹₆₀ h
50 min = ⁵⁰₆₀ h = ⁵₆ h
3 h 50 min = 3⁵₆ h

Distance that Mr Fong drove
= 3⁵₆ x 90
= 345 km

Distance that Mrs Fong drove when Mr Fong reached
= 345 - 14 
= 331 km

Time that Mrs Fong took to travel from 10 a.m. to 3 p.m. = 5 h

Mrs Fong's average speed
= 331 ÷ 5
= 66¹₅ km/h

Answer(s): 66¹₅ km/h