To solve this problem you must apply the proccedure shown below:
1. You have the following expression:
(3+3i)-(13+15i)
2. If you want to substract both terms, you need to substract the real numbers and the complex numbers. Then, you obtain:
3+3i-13-15i
(3-13)+(3i-15i)
3. Then, you obtain the following result:
-10-12i
4. Therefore, as you can see, the correct answer is the last option (option D), which is:
D. -10-12i