We need to know the alcohol content of your beer before we can give you an accurate answer. The answers above are based on adding the alcohol to water, and fail to take into account any alcohol that may already be in the beer.
The differences are probably pretty minor, but to illustrate - if you were to pour the whiskey into a beer that was already 99% alcohol, you would actually be lowering the alcohol content of your mix. A silly example, but it proves the point.
So, if you want an accurate answer, we need to know the aldohol content of your beer before the addition. It probably won't make a 1/10% difference from what has already been submitted, but it is required to do the math correctly.