[tex]a+b=7 \\ 3a=5+b \ sau \ b+5=3a \to \fbox{b=3a-5} \\ ************************\\ \\ a+3a-5=7\\4a-5=7\\4a=7+5\\4a=12 \\ a=12:4\\ \boxed{\bold{a=3}} \\ \\ b=3*3-5\\ a=9-5\\ \boxed{\bold{a=4}} [/tex]
[tex]\text{Verificare:} \\ 3+4=7 \ (\text{A})\\ \\ 3*3=4+5\\9=9 \ (\text{A})[/tex]
