\[px + py - 5x - 5y =\]
\[= p(x + y) - 5 \cdot (x + y) =\]
\[= (x + y)(p - 5).\]
\[Проверка:\]
\[(x + y)(p - 5) =\]
\[= px - 5x + py - 5y = \ \]
\[= px + py - 5x - 5y.\]