\[4a + by + ay + 4b =\]
\[= 4a + ay + 4b + by =\]
\[= a(4 + y) + b(4 + y) =\]
\[= (4 + y)(a + b).\]
\[Проверка:\]
\[(4 + y)(a + b) =\]
\[= 4a + 4b + ay + by =\]
\[= 4a + by + ay + 4b.\]