Looking for help calculating a probability formula
Ok, I am not sure if I understood it correctly. But if it is only the right-side figure equation it would be:

=1/(1+EXP(3.1058))


(I have tested on LibreOffice only, but it should work on excel as well)

Now, if you want to do something more complex using the prior knowledge of event A, it should be more clear what is exactly this event and how it is related to the equation.

(I am relly not sure it this is what you want, so if it is not, I apologize)