Alright, I'll give it a try ....
Painting the 1st half of the 32 square metres took 1/8 of a 2-litre tin of paint. That's 1/4 of a litre of paint.
Painting the 2nd half of it will take the same amount as the 1st half did, or 1/4 of a litre.
So it'll take a total of 1/2 a litre of paint to do 1 coat of the 1st room.
And you want to do a 2nd coat of that room, so that'll take another 1/2 a litre of paint.
Then you want to do a 1st coat of the 48 square metres room, which is 50% bigger than the 32 square metres room.
So that'll take 50% more paint than was needed to coat the 1st room (which took 1/2 of a litre). So that'll take 3/4 of a litre.
So you'll have used 1/2 a litre of paint on the 1st room, and 3/4 of a litre on the 2nd room, for a total of 1 and 1/4 litres.
So in the end, there'll be 3/4 of a litre, or 750 mls, of paint left in your 2-litre tin.