y=x-1
x+y=3
use substitution
sub the first into the second
x + x-1 = 3
2x = 4
x = 2
sub that back into the first equation
y = 2-1
y = 1
x+y=3
sub the first into the second
x + x-1 = 3
2x = 4
x = 2
sub that back into the first equation
y = 2-1
y = 1