The correct answer is the option "B":
B.(-x-6i)(x-6i)
Explanation
You must keep in mind the following:
1. By definition, a complex number has the following form:
a+bi
"a" is the real part and "b" is the imaginary part.
2. i²=-1
3. Then,you have:
(-x-6i)(x-6i)=(-x²+(6i)²)=-x²-36
4. Therefore, the answer is: (-x-6i)(x-6i)