18 units of alcohol in the wine (assuming 75 cl bottles) and 13.125 units in the vodka (assuming 35 cl for a half bottle) the ABV is just what percentage by volume is alcohol. To calculate units multiply the amount in ml by the abv and divide by 1000.
Fitzer needs to check his/her sums! The wine has 19.5 units.
An easy way to look at it is that the '%abv' figure tells you how many units there are in 1 litre of the drink. 2 bottles of wine comes to 1� litres. So that's 1� lots of 13 units = 19� units.
Similarly, a full litre of vodka would contain 37.5 units. A half bottle holds just over a third of a litre, so that's just a bit more than a 12� units. (Fitzer has done the accurate sum for you).