\[a \cdot (4a - 5)(2a + 3) =\]
\[= \left( 4a^{2} - 5a \right)(2a + 3) =\]
\[= 8a^{3} + 12a^{2} - 10a^{2} - 15a =\]
\[= 8a^{3} + 2a^{2} - 15a\]