[tex]\displaystyle\bf\\a+4b=30,~4b~este~mereu~par,~oricare~ar~fi~b~numar~natural.\\dar,~30~este~par,~si~cum~4b~este~par~rezulta~ca~a~este~par,~dar~a~este~\\prim,~deci~\boxed{\bf a=2}~.\\atunci,~:~2+4b=30 \Leftrightarrow 4b = 28 \Leftrightarrow~\boxed{\bf b=7}~.[/tex]
