\[16 - (y + 1)^{2} = \left( 4 - (y + 1) \right) \cdot\]
\[\cdot \left( 4 + (y + 1) \right) = (4 - y - 1) \cdot\]
\[\cdot (4 + y + 1) = (3 - y)(5 + y)\]