I'd suggest re-wording your question:
"How do I find the ordered pair (x,y) that solves this system of linear equations?"
One way of doing that would be to substitute y=5x+7 into the other equation:
-3x - 2(5x+7) = -12. Solve this for x. Once you have a value for x, subst. that value into y=5x+7 to find the corresponding y value.
Then write the ordered pair (x,y). That's it.
