1. The problem is to simplify the expression $6 \sqrt{13}$. 2. Recall that $\sqrt{a}$ represents the square root of $a$, and it cannot be simplified further if $a$ is not a perfect square. 3. Since 13 is a prime number and not a perfect square, $\sqrt{13}$ cannot be simplified further. 4. Therefore, the expression $6 \sqrt{13}$ is already in its simplest form. Final answer: $6 \sqrt{13}$