To apply the operation $\S$ to 7 and 2, I need to plug in 7 for $a$ and 2 for $b$ in the formula $3a+5b$. So, $7\,\S\,2=3(7)+5(2)$. $3(7)+5(2)=21+10=31$. 
Define the operation $\S$ as follows: $a\,\S\, b=3a+5b$. What is the value of $7\,\S\,2$?