You didn't really ask a question, so I'm assuming you want to know if there are any solutions to BOTH equations.
Use the first equation to substitute 4x - 1 for y in the second equation:
12x = 3(4x - 1)+7
12x = 12x - 3 + 7
12x = 12x +4
0 = 4
The last equation is FALSE, indicating the system of two equations has no solution.