Rewrite the equations:
X-Y=-15
X+Y=160 because 145+15=160.
Now, add the two equations:
2X=160-15=145, X=145/2.
X+Y=160 becomes Y=160-X=160-145/2=(320-145)/2=175/2.
So the solution is X=145/2 and Y=175/2.
Or, X-Y=-15 becomes Y=X+15=145/2+15=(145+30)/2=175/2.