10 litres ;)
1/10 x 3/10 = 4/100
5/10 x 5/10 = 25/100
1/10 x 5 = 5/10
(3/10 divided by 3) x5 = 5/10
5y = 5x/3
15y = 5x <-- 20 altogether
40 divided by 20 = 2
2x5 = 10litres
2x15 = 30litres
(Sorry it's written really weirdly, I can't type anything on my phone x'D )