Answer: C is the correct answer.
Step-by-step explanation: First of all, you have to eliminate the answer choice in which the angles are different for the cosine term and for the sine term. Therefore, you can eliminate choice D.
The way that complex numbers are written are the following:
z=a+bi
r (which is considered the magnitude/number outside the parentheses)=sqrt (a^2+b^2)
tan(angle)=b/a.
Now using the information given here,
a=-6, b=6.
r=sqrt ((-6)^2+6^2)=sqrt(72)=6sqrt2
tan(angle)=6/-6=>-1
angle is equal to arctan(-1)=3pi/4.
Therefore the correct answer is C. Hope that helped!