You need to notice that if you add the equations, the variable y will be eliminated, hence, performing the addition of equations, yields:

`2x + y + x - y = 15 + 45`

Reducing duplicate terms yields:

`3x = 60 => x = 60/3 => x = 20`

Substituting 20 for x in the equation `x - y = 45` yields:

`20 - y = 45 => -y = 45 - 20 => -y = 25 => y = -25`

Hence, evaluating the solution to the system, using elimination method, yields `x = 20, y = -25.`