Question 5239
Let x = number of litres (English spelling) required.

(3360*x) + (1120*12) = 1680*(12+x)
3360x + 13440 = 20160 + 1680x
3360x - 1680x = 20160 - 13440
1680x = 6720
x = 6720/1680
x = 4litres


jon.