Without a diagram, one must make certain assumptions about this problem. If and only if these three angles are the interior angles of a triangle, then their sum must be 180 degrees, so that 18x+12 + 6y + 3x+4y = 180. Unfortunately, this is a single equation in 2 unknowns. Thus, we cannot solve for an explicit value for either x or y.
If there was a diagram, please share it; otherwise, describe the triangle in words as best you can.