Mrs Ma left home at 10 a.m. and drove towards the city. 1¹₄ hour later, Mr Ma left the house and drove at an average speed of 87 km/h towards the city. When Mr Ma reached his destination at 2 p.m., Mrs Ma was 30 km away from the city. Find Mrs Ma’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
¹₄ h = ¹₄ x 60 = 15 min
1¹₄ = 1 h 15 min

1 h 15 min after 10 a.m. = 11.15 a.m.

Time that Mr Ma left the house = 11.15 a.m.

Time that Mr Ma took from 11.15 a.m. to 2 p.m. to reach his destination = 2 h 45 min

1 min = ¹₆₀ h
45 min = ⁴⁵₆₀ h = ³₄ h
2 h 45 min = 2³₄ h

Distance that Mr Ma drove
= 2³₄ x 87
= 239¹₄ km

Distance that Mrs Ma drove when Mr Ma reached
= 239¹₄ - 30 
= 209¹₄ km

Time that Mrs Ma took to travel from 10 a.m. to 2 p.m. = 4 h

Mrs Ma's average speed
= 209¹₄ ÷ 4
= 52⁵₁₆ km/h

Answer(s): 52⁵₁₆ km/h