How many goals does Barcelona have to score against Inter during the semi final to reach the UEFA finals?

I know Inter leads 3-1


I also know the 2nd leg is being played at home barcelona|||Barcelona only need to score 2 goals. It will then be 3-3 on agg. Because Barca have an away goal, that will put them through. However, any other score line will determine who wins. If the game goes 3-1 to Barca, extra time and penalties will be played.