Intro to three phase systems - 1

A symmetrical three-phase electrical system has the phase sequence BAC and $V_c = 220 \angle{60^{\circ}}$ find $V_a$ and $V_b$ . If $\theta$ and $\phi$ are the angles for $V_a$ and $V_b$ , what is $\theta + \phi$ ?

Details and assumptions:

$0^{\circ} \le \theta \le 360^{\circ}$

$0^{\circ} \le \phi \le 360^{\circ}$

$\theta$ and $\phi$ are in degrees.