Question

a) x+y=5
X-y=-1
b) 2x-3y=5
-2x+y=-1
c) 3x-y=4
2x+2y=0

Answer 1

x+y=5
x-y=-1
__________
2x=4
x=2
y=5-2=3

2x-3y=5
-2x+y=-1
_______
-2y=4
y=-2
x=(-1+2):(-2)=-1/2

3x-y=4              I*2          
2x+2y=0

6x-2y=8
2x+2y=0
_________
8x=8
x=1

y=3-4=-1