That is not the answer. I want to know the magnitude and phase of Vx1x2 and Vx4x3 in a split phase system.
Staying with the picture RonaldRC provided, since I often can't see yours.
Presuming the standard convention of + to - being <0; Presuming V12 therefore to be +120<0; We now have two cases:
1) As pictured with a primary coil V34 = +120<0 and therefore V14 = V12 + V34; Placing you leads backward to get V43 fails to match polarity with your circuit. Therefore you fail your quiz.
2) Ignoring the presence of the primary coil; What would you like? V34 = +120<0 or V43 = -120<180? So V14 = V12 + V34 = V12 - V43. Your choice. Have fun. Don't be an engineer.