To start this, get an equation in terms of one variable - lets choose the first one
-x+y=4 ---> y=4+x
now we plug this into the second equation
3x-2(4+x)=-7
we can now simplify that equation in order to get a numeric value for our x variable
3x-2(4+x)=-7 ---> 3x-8-2x=-7 ---> x-8=-7 ---> x=1
now we can plug that value into one of the original equations in order to solve for y
-1+y=4 ---> y=5
