Your work is correct!
Here's another approach . . .
I tried to solve this two equations using substitution
but my x's ended up canceling out when trying to solve for x.
Graphic solution: we want the intersection of the two lines.
We have two lines: one has y-intercept -7, the other has y-intercept 4.
Both have slope 3 . . . The lines are parallel.
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Obviously, the line do not intersect.
Therefore, the system has no solution.