t = nr. vaselor de 3 litri
z = nr. vaselor de 10 litri
t + z = 12~~| × (-3)
3t + 10z = 71
---
-3t - 3z = -36
3t + 10z = 71
------------------------ adunam ecuatiile
/ 7z = 35
z = 35 : 7 = 5 vase de 10 litri
t + z = 12
t = 12 - z = 12 - 5 = 7 vase de 3 litri