Mrs Oh left home at 7 a.m. and drove towards the city. 1⁵₆ hour later, Mr Oh left the house and drove at an average speed of 84 km/h towards the city. When Mr Oh reached his destination at 3 p.m., Mrs Oh was 27 km away from the city. Find Mrs Oh’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
⁵₆ h = ⁵₆ x 60 = 50 min
1⁵₆ = 1 h 50 min

1 h 50 min after 7 a.m. = 8.50 a.m.

Time that Mr Oh left the house = 8.50 a.m.

Time that Mr Oh took from 8.50 a.m. to 3 p.m. to reach his destination = 6 h 10 min

1 min = ¹₆₀ h
10 min = ¹⁰₆₀ h = ¹₆ h
6 h 10 min = 6¹₆ h

Distance that Mr Oh drove
= 6¹₆ x 84
= 518 km

Distance that Mrs Oh drove when Mr Oh reached
= 518 - 27 
= 491 km

Time that Mrs Oh took to travel from 7 a.m. to 3 p.m. = 8 h

Mrs Oh's average speed
= 491 ÷ 8
= 61³₈ km/h

Answer(s): 61³₈ km/h