First you would need to have your X"s kill themselves or the Y's either one does matter.To kill you need to have a negative and a positive X or Y. For example

X+Y=11

3x-Y=5

For this equation you find that the Y's can cancel out. You get

4x=16

Dividing the 4x by bothsides you get.

X=4

Substituting the X=4 in the eqation you get 4+y=11. Now you find this to be a simple equation.

Your answer you'll find is X=4 and y=7

X+Y=11

3x-Y=5