\[2 \cdot (b + 1)(b + 3) =\]
\[= 2 \cdot (b \cdot b + 3b + b + 3) =\]
\[= 2 \cdot \left( b^{2} + 4b + 3 \right) =\]
\[= 2b^{2} + 8b + 6.\]