\[(3x - 1)(8b + 1) + (7b - 3)(1 - 3x) =\]
\[= (3x - 1)(8b + 1) - (7b - 3)(3x - 1) =\]
\[= (3x - 1)\left( 8b + 1 - (7b - 3) \right) =\]
\[= (3x - 1)(8b + 1 - 7b + 3) =\]
\[= (3x - 1)(b + 4).\]