>I need to know what 4!! equals

4!! = 4·2

For any number n, n!! means the product of the decreasing sequence of natural numbers that starts with n and inlcudes every other number:

7!! = 7·5·3·1
8!! = 8·6·4·2
9!! = 9·7·5·3·1

> and how you reached the
> answer

What answer?