How do you solve by substitution #y = 3x – 4# and #9x – 3y = 14#?
These equations represent parallel lines so there is no solution.
We can attempt a solution as follows:
Using , substitute
So, what went wrong?
If we take  and rearrange it into standard form:
then multiplying by 3
What are we to make of the combination of  and ?
If we graph these two equations, we would see that they form a pair of parallel lines. (Go ahead; try it. I'll wait).
If two lines are parallel then they do not intersect and there is no point where they are equal.