The simultaneous equation has no solution
How to solve the equation by substitution
The given equations are
x = y - 1,
-x + y = -1
substitute x = y - 1, into -x + y = -1
-x + y = -1
-(y - 1) + y = -1
-y + 1 + y = -1
1 = -1
The simultaneous equaiton is inconsistent