Question

How do you solve by substitution `y = 3x - 7` and `6x - 2y = 12`?

Answer 1

We know that `color(red)(y=3x-7)`

Thus :

`6x-2color(red)y=12`
`6x-2color(red)((3x-7)=12`
`cancel(6x)-cancel(6x)+14=12`
`14=12`

Nonsense.
There is thus no solution to this equation.