\[\boxed{\text{69\ (69).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\textbf{а)}\ x + a \cdot b\]
\[\textbf{б)}\ a\ :(b - c)\]
\[\textbf{в)}\ (x + a) \cdot (x - b)\]