We know that \[\left( a\text{ }+\text{ }b \right)3\text{ }=\text{ }a3\text{ }+\text{ }3a2b\text{ }+\text{ }3ab2\text{ }+\text{ }b3\]

Putting\[a\text{ }=\text{ }3×2\text{ }\And \text{ }b\text{ }=\text{ }-a\text{ }\left( 2x-3a \right)\] , we get

\[\left[ 3×2\text{ }+\text{ }\left( -a\text{ }\left( 2x-3a \right) \right) \right]3\] \[=\text{ }\left( 3×2 \right)3+3\left( 3×2 \right)2\left( -a\text{ }\left( 2x-3a \right) \right)\text{ }+\text{ }3\left( 3×2 \right)\text{ }\left( -a\text{ }\left( 2x-3a \right) \right)2\text{ }+\text{ }\left( -a\text{ }\left( 2x-3a \right) \right)3\]

\[=\text{ }27×6\text{ }\text{ }27ax4\text{ }\left( 2x-3a \right)\text{ }+\text{ }9a2x2\text{ }\left( 2x-3a \right)2\text{ }\text{ }a3\left( 2x-3a \right)3\]

\[=\text{ }27×6\text{ }\text{ }54ax5\text{ }+\text{ }81a2x4\text{ }+\text{ }9a2x2\text{ }\left( 4×2-12ax+9a2 \right)\text{ }\text{ }a3\text{ }\left[ \left( 2x \right)3\text{ }\text{ }\left( 3a \right)3\text{ }\text{ }3\left( 2x \right)2\left( 3a \right)\text{ }+\text{ }3\left( 2x \right)\left( 3a \right)2 \right]\]

\[=\text{ }27×6\text{ }\text{ }54ax5\text{ }+\text{ }81a2x4\text{ }+\text{ }36a2x4\text{ }\text{ }108a3x3\text{ }+\text{ }81a4x2\text{ }\text{ }8a3x3\text{ }+\text{ }27a6\text{ }+\text{ }36a4x2\text{ }\text{ }54a5x\]

\[=\text{ }27×6\text{ }\text{ }54ax5+\text{ }117a2x4\text{ }\text{ }116a3x3\text{ }+\text{ }117a4x2\text{ }\text{ }54a5x\text{ }+\text{ }27a6\]

Thus, \[\left( 3×2\text{ }\text{ }2ax\text{ }+\text{ }3a2 \right)3\]

\[=\text{ }27×6\text{ }\text{ }54ax5+\text{ }117a2x4\text{ }\text{ }116a3x3\text{ }+\text{ }117a4x2\text{ }\text{ }54a5x\text{ }+\text{ }27a6\]