\[(3p - 2k)(2k + 3p) - (3p - k)^{2} =\]
\[= (3p - 2k)(3p + 2k) - \left( 9p^{2} - 6pk + k^{2} \right) =\]
\[= 9p^{2} - 4k^{2} - 9p^{2} + 6pk - k^{2} =\]
\[= - 5k^{2} + 6pk = k \cdot (6p - 5k).\]