Let $a\oplus b=3a+4b$ for all real numbers $a$ and $b$.  Find $3\oplus 1$.
To find $3\oplus 1$, I need to plug in $a=3$ and $b=1$ into the definition of $a\oplus b$. That gives me $3\oplus 1=3(3)+4(1)$. I can simplify this by doing the arithmetic: $3\oplus 1=9+4=13$. 