Transformer output voltage equations?
Here is a picture of what happens in order to help you find the rest of the formulas: -



It's easy to just let you have all the formulas but it's a learning process best undertaken with half-help. Call me mean if you will.

If Rs is a significant value (not usually that critical to simple power supplies) then you'll need to factor that is but if it's a small percentage of the DC load then ignore for now.