2x + y = 10

y = - 2x + 8

By using substitution, this equation will be easy to solve. Plug the second equation into the first equation and solve like you normally would to find x, then use that x value to plug it into y.

2x + (-2x+8) = 10

8=10

In this case, the variable was cancelled out itself, which means that this problem is undefined.

you cant solve.