Minimizing a Product of Two Expressions

For positive real numbers $a$ and $b$, the minimum value of $$\left(18a+\frac{1}{3b}\right)\left(3b+\frac{1}{8a}\right)$$can be expressed as $\frac{m}{n}$, where $m$ and $n$ are relatively prime positive integers. The value of $m+n$ is