I acvariu --- 1,5x litri
II acvariu --- x+5 litri in total 61 litri
III acvariu --- x litri
1,5x+x+5+x=61; 3,5x=61-5; 3,5x=56; x=16 litri (III acvariu)
II acvariu: 16+5=21 litri
I acvariu: 16·1,5=24 litri
Raspuns: I --- 24 litri; II --- 21 litri; III --- 16 litri