Answer :
I can solve by subsituttion
x+y=8
y=8+x
subsitute 8+x for y
x+8+x=8
2x+8=8
subtract 8 from both sdies
2x=0
x=0
subsitute
0+y=8
y=8
x=0
y=8
x+y=8
y=8+x
subsitute 8+x for y
x+8+x=8
2x+8=8
subtract 8 from both sdies
2x=0
x=0
subsitute
0+y=8
y=8
x=0
y=8