If you have a problem such as a·cos(A) / b·cis(B)
you can solve it as: (a/b)·cis(A - B)
For this problem a = 12 and b = 4·sqrt(6) so a/b = sqrt(6)/2
and A = 7pi/6 and B = 3pi/4 so A - B = 5pi/12
Therefore, the answer is: sqrt(6)/2·( cos(5pi/12) + i·sin(5pi/12) )