last problem 100% of my next grade please help anyone

Answer:
z =-8.660254038 -5i
Step-by-step explanation:
z = |z| cos theta + |z| i sin theta
We know |z| and theta
z = 10 cos 210 +10 i sin 210
z = 10 (-sqrt3)/2 + 10i (-1/2)
z = -5 sqrt(3) -5i
or approximately
z =-8.660254038 -5i