Find the digits

let the digits be $a, b$ and $c$ with $0\le a\le b\le c<10$ . The difference between the biggest and smallest number then becomes $100c+10 b+a-100 a-10 b-c=99 c-99 a=396\Longleftrightarrow c-a=4$ . And since the sum of the digits is 15, $a+b+c=15\Longleftrightarrow a+b+(a+4)=15\Longleftrightarrow a+b/2=5.5$ . The only solutions with $b$ beeing uneven and $a\le b\le a+4$ is $(a,b)=(3,5)$ . Therefore the digits are $3,5$ and $7$ .