Mrs Kong left home at 8 a.m. and drove towards the city. 1¹₆ hour later, Mr Kong left the house and drove at an average speed of 90 km/h towards the city. When Mr Kong reached his destination at 1 p.m., Mrs Kong was 23 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 8 a.m. = 9.10 a.m.

Time that Mr Kong left the house = 9.10 a.m.

Time that Mr Kong took from 9.10 a.m. to 1 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 Kong drove
= 3⁵₆ x 90
= 345 km

Distance that Mrs Kong drove when Mr Kong reached
= 345 - 23 
= 322 km

Time that Mrs Kong took to travel from 8 a.m. to 1 p.m. = 5 h

Mrs Kong's average speed
= 322 ÷ 5
= 64²₅ km/h

Answer(s): 64²₅ km/h