Number of subsets of (x,y) is:

Number of subsets of (x,y) is:

Explanation
 The number of subsets of a set with 2 elements, such as (x, y), is 2^2 = 4.
Here are the 4 subsets:
1. {} (the empty set)
2. {x}
3. {y}
4. {x, y} (the original set itself)
This is because each element (x and y) can either be included or excluded from the subset, giving us 2 options for each element, and therefore 2^2 = 4 total subsets.