[tex]\displaystyle\\
\overline{xy}=3x+5y\\\\
10x+y=3x+5y\\\\
10x-3x =5y-y\\\\
7x=4y\\\\
\Longrightarrow~~\boxed{\bf x=4~~si~~y=7}\\\\
\text{Probe:}\\
7\cdot 4 = 4\cdot 7 = 28\\\\
\overline{xy}=3x+5y~~\Leftrightarrow~~\overline{47} = 3\cdot4+5\cdot7=12+35 = 47
[/tex]
