X + y = 27
x = y + 3
y + 3 + y = 27
2y + 3 = 27
2y = 27 - 3
2y = 24
y = 24/2
y = 12
x = y + 3
x = 12 + 3
x = 15
ur numbers are 12 and 15
The additive identity property states that for every number a, you have

You're showing this property when you write

The solution is:
y = 3
and
x = 5