x = numar de galeti de 20 litri
y = numar de galeti de 15 litri
.
[tex]\displaystyle\bf\\x=3y\\20x+15y=675 \\- - - - -\\20\cdot 3y+15y=675\\60y+15y=675\\75y=675\\\\y=\frac{675}{75}\\\\\boxed{\bf y=9~galeti~de~15~litri~zilnic}\\x=3y\\x=3\cdot9\\\boxed{\bf x=27~galeti~de~20~litri~zilnic}[/tex]