alcohol concentration

Hello all! This is my first ever attempt to homebrewing cider! I have been letting the apple juice and yeast ferment for two weeks and went to check the specific gravity with my hydrometer. From what I have read there should be at least some alcohol content by now however, it is reading zero...

Does anyone know how to calculate the following information: I added 150 ml of vodka tincture (orange peels soaked in vodka) to 6 gallons of beer in the fermenter. The vodka is 40% (80 proof). I just need to know how much this will increase the abv for the 6 gallons? I've read...