The ratio shown in fraction form would be;

Now to convert it to its simplest form, you need to find their greatest common factor; (so in this case it would be 28...cause 28 goes into 56 evenly)
*Now divide both terms by
28
28 ÷ 28 =
1
56 ÷ 28 =
2
so your ratio 28 to 56 in simplest form is..

Hope this helps :)
X is always dependant to Y. so that should answer the 1st one. the 2nd looks to be around 17-18. 17.5 maybe. and the 3rd is yes cause he does not go to the pool so it isnt any cost.
A common factor of both 126 and 399 is 3 so we can divide both numbers by 3.
126 / 3 = 42
399 / 3 = 133
A common factor for both 42 and 133 is 7 so we can divide both numbers by 7.
42 / 7 = 6
133 / 7 = 19
19 is a prime number so we can't reduce it anymore, therefore 126/399 in its simplest form is 6/19