\[4b(3b + 6) - (3b - 5)(3b + 5) =\]
\[= 12b^{2} + 24b - \left( 9b^{2} - 25 \right) =\]
\[= 12b^{2} + 24b - 9b^{2} + 25 =\]
\[= 3b^{2} + 24b + 25.\]