If this is a system of equations then:
Multiply 5x-y=3 by -2
=> -10x+2y=-6
Now you sum the equations:
10x-10x+7y+2y=-3-6
=> 9y=-9
Then just divide by 9: y=-1
Now to get x, choose one of the equations and use the value we got from y:
5x-(-1)=3 => 5x+1=3 => 5x=3-1
=> 5x=2
=> x=2/5
(x,y)=(2/5, -1)
