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X+y=30
Y+z=15
2x+7y+5z=?
Coronita (:


Răspuns :

[tex]2x+7y+5z= \\ \\ =2x+2y+5y+5z= \\ \\ =2(x+y)+5(y+z)= \\ \\ =2 \cdot 30 + 5 \cdot 15= \\ \\ =60+75= \\ \\ =\boxed{135}[/tex]