[tex] \left \{ {{2a+3b=90|(-1)=\ \textgreater \ \left \{ {{-2a-3b=-90} \atop {4a-3b=120}} \right. } \atop {4a+3b=120}} \right. \\
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2a=30=\ \textgreater \ a=30:2=\ \textgreater \ a=15lei[/tex]
Un bilet de film este 15 lei.
a = film
b = teatru.