x-numarul de mese cu 2 locuri
y-numarul de mese cu 3 locuri
[tex] \left \{ {{x+y=35} \atop {2x+3y=90}} \right. [/tex] [tex] \left \{{{x=35-y} \atop {2(35-y)+3y=90}} \right. |⇒ \left \{ {{x=35-y} \atop {70-2y+3y=90}} \right. |⇒ \left \{ {{x=35-y} \atop {y=20}} \right.| ⇒ \left \{ {{y=20} \atop {x=35-20}} \right. |⇒ \left \{ {{y=20} \atop {x=15}} \right. [/tex]