Step-by-step explanation:
The usual thing to do is to try to get rid of one variable first. So to get rid of x, we multiply the first equation by 5.
5(x + y) = 2(5)
-5x - 5y = -10
---> 5x + 5y = 10
-5x - 5y = -10
---> 0 = 0
As you can see, everything cancels out. If the statement is true, then it is infinitely many solutions.