Answer:
The answer is B.
Explanation:
This is because decreased means subtraction.
Also, it would be A if it would say "5 decreased by n."
It means that a number is being decreased by 5.
For example, "10 cookies decreased by 5 cookies." That means that the original was 10 cookies, and then someone ate 5, so there was 5 left. It doesn't mean that there was 5 and then someone added 5.
Hope this helps!