The constraint \( 3x + 4y \leq 12 \) represents a line with the x-intercept \( x = 4 \) and the y-intercept \( y = 3 \).
By evaluating the value of \( Z = x + y \) at each of the vertices of the feasible region, we find that the maximum value occurs at \( (0, 6) \) where \( Z = 6 \).
Thus, the correct answer is \( (0, 6) \).