\[(2b + 5)^{2} - (b - 3)(3b + 5) =\]
\[= 4b^{2} + 20b + 25 - \left( 3b^{2} - 9b + 5b - 15 \right) =\]
\[= 4b^{2} + 20b + 25 - 3b^{2} + 4b + 15 =\]
\[= b^{2} + 24b + 40.\]