Here's a property of exponents.

We have to simplify

Use the property of exponents I have shown.

You chose the right answer. Good job! Hope this helps! :)
One very simple way is to put it in a Ti-84 calculator which shows that cos(105) is -0.2409590492 and sin(15) as 0.6502978402 which you can find online.
Answer:
What is 20 percent of 500.? = 100.
Step-by-step explanation: