Mrs Goh left home at 7 a.m. and drove towards the city. 1²₃ hour later, Mr Goh left the house and drove at an average speed of 93 km/h towards the city. When Mr Goh reached his destination at 1 p.m., Mrs Goh was 18 km away from the city. Find Mrs Goh’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
²₃ h = ²₃ x 60 = 40 min
1²₃ = 1 h 40 min

1 h 40 min after 7 a.m. = 8.40 a.m.

Time that Mr Goh left the house = 8.40 a.m.

Time that Mr Goh took from 8.40 a.m. to 1 p.m. to reach his destination = 4 h 20 min

1 min = ¹₆₀ h
20 min = ²⁰₆₀ h = ¹₃ h
4 h 20 min = 4¹₃ h

Distance that Mr Goh drove
= 4¹₃ x 93
= 403 km

Distance that Mrs Goh drove when Mr Goh reached
= 403 - 18 
= 385 km

Time that Mrs Goh took to travel from 7 a.m. to 1 p.m. = 6 h

Mrs Goh's average speed
= 385 ÷ 6
= 64¹₆ km/h

Answer(s): 64¹₆ km/h