87. If the prime number $m<n$, the sum of all proper fractions with $m$ as the denominator is denoted as $A$. The sum of all proper fractions with $n$ as the denominator is denoted as $B$. If $A \times B=5$, then $m=$ $\qquad$ , $n=$ $\qquad$ .
Reference answer: 3,11