IS. $3 W$ and $F$ are two integers which are greater than 20. If the product of $W$ and $F$ is $b$ and the sum of $W$ and $F$ is $c$, find the value of $c$.
$\begin{array}{l}\left\{\begin{aligned} W F & =770 \cdots \cdots(1) \\ W+F & =c \quad \cdots \cdots(2)\end{aligned}\right. \\ 770=22 \times 35 \\ W=22, F=35 \\ c=22+35=57 \\\end{array}$