The answer is y-x because there are y seats and x people leave and the key word is leave. When there is words like leave or less those give you hints that mean you are subtracting.
2.5 m =2.5*100=250 cm
So the ratio is
250:60
25:6
1:(6/25)
n=6/25
The answer for your question 186.
The distance between them is 9.