Polar Coordinates and Complex Numbers · Hard problem

$\ 12\left(\cos120^\circ+i\sin120^\circ\right)$

$-\ 6\left(\cos120^\circ+i\sin120^\circ\right)$

$\ 6\left(\cos120^\circ+i\sin120^\circ\right)$

$\ 7\left(\cos120^\circ+i\sin120^\circ\right)$