SG. 3 If $c$ is a 2 digit positive integer such that sum of its digits is 10 and product of its digit is 25 , find the value of $c$. (Reference: 1997 FG5.3)
$$
\begin{array}{l}
c=10 x+y, \text { where } 0<x<10,0 \leq y<10 . \\
x+y=10 \\
x y=25
\end{array}
$$

Solving these two equations gives $x=y=5 ; c=55$