$a) 3x - 2y + xy = 17
\\\Leftrightarrow xy+3x-2y-6=11
\\\Leftrightarrow x(y+3)-2(y+3)=11
\\\Leftrightarrow (y+3)(x-2)=11$
.............................
$b)\dfrac{x-11}{y-10}=\dfrac{11}{10}=\dfrac{x-11+11}{y-10+10}=\dfrac{x}{y}
\\\Rightarrow \dfrac{x}{11}=\dfrac{y}{10}=k\Rightarrow x=11k;y=10k
\\\Rightarrow |x-y|=|11k-10k|=|k|=12\Rightarrow k=\pm 12
\\\Rightarrow x=132;y=120 \ or \ x=-132;y=-120$