Let the sum of two positive integers be 24. If the probability, that their product is not less than 3/4 times their greatest possible product, is…

Let the sum of two positive integers be $\displaystyle 24$ . If the probability, that their product is not less than $\displaystyle \frac{3}{4}$ times their greatest possible product, is $\displaystyle \frac{m}{n}$, where $\displaystyle \operatorname{gcd}(m, n)=1$, then $\displaystyle n-m$ equals