jmc

Let $n$, $n+1$, and $n+2$ be the lengths of the sides of the triangle. Then the perimeter of the triangle is $n+(n+1)+(n+2)=3n+3$. Using the fact that the length of the smallest side is $30\%$ of the perimeter, it follows that: $n=0.3(3n+3)\Rightarrow n=0.9n+0.9\Rightarrow 0.1n=0.9\Rightarrow n=9$. The longest side is then $n+2=11$. Thus, answer choice $\boxed{11}$ is correct.