Mrs Kong left home at 9 a.m. and drove towards the city. 1¹₆ hour later, Mr Kong left the house and drove at an average speed of 85 km/h towards the city. When Mr Kong reached his destination at 3 p.m., Mrs Kong was 15 km away from the city. Find Mrs Kong’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 9 a.m. = 10.10 a.m.

Time that Mr Kong left the house = 10.10 a.m.

Time that Mr Kong took from 10.10 a.m. to 3 p.m. to reach his destination = 4 h 50 min

1 min = ¹₆₀ h
50 min = ⁵⁰₆₀ h = ⁵₆ h
4 h 50 min = 4⁵₆ h

Distance that Mr Kong drove
= 4⁵₆ x 85
= 410⁵₆ km

Distance that Mrs Kong drove when Mr Kong reached
= 410⁵₆ - 15 
= 395⁵₆ km

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

Mrs Kong's average speed
= 395⁵₆ ÷ 6
= 65³⁵₃₆ km/h

Answer(s): 65³⁵₃₆ km/h