Question

x+y=3
2x-2y=1 resolver

Answer 1

a_x+y=3
     x=3-y
b_2x-2y=1
    2x=1+2y
    x=1/2+y

Answer 2

x=3-y
2*(3-y)-2y=1
6-2y-2y=1
-4y=-5 ...*(-1)
4y=5
y=5/4

y=3-x
2x-2*(3-x)=1
2x-6+2x=1
4x=7
x=7/4