The answer is 2/3
10 / 5 = 2
15 / 5 = 3
= 2/3
To solve this problem you must apply the proccedure shown below:
If
, you have that:

Because
and 
Therefore, as you can see, the answer is: 
One of Y is the same amount as two of x...for example if y is equal to 10, x is equal to 5