C is incorrect, which is the correct answer?

The marketing department requests that the professional printer units shall be at least three times of the standard printer units. Which of the following is the equation of this new constraint? Decision Variables: *1: units of standard printer produced x 2: units of professional printer produced Objective function: Maximize the total profit Z: 15x1 + 20x2 Constraints: Machine: 3x1 + 10x2 = 500 Non-negativity: x1, x2 >=0 None of the choices is correct. -0.3X1 + 0.7X2 =0 -3X1 + x2 >=0