[tex]({ { 6x }^{ 5 }) }^{ -3 }[/tex]
Rule : [tex]{ (x\cdot y) }^{ a }\quad =\quad { x }^{ a }\cdot { y }^{ a }[/tex]
So if we apply this rule to the expression :
[tex]({ { 6x }^{ 5 }) }^{ -3 }\quad =\quad { 6 }^{ -3 }\cdot { x }^{ 5\cdot -3 }\quad =\quad { 6 }^{ -3 }\cdot { x }^{ -15 }[/tex]
[tex]\boxed { { 6 }^{ -3 }\cdot { x }^{ -15 } } [/tex]
Let's rewrite the expression
[tex]\frac { 1 }{ { 6 }^{ 3 } } \cdot \frac { 1 }{ { x }^{ 15 } } \quad =\quad \frac { 1 }{ { 6 }^{ 3 }\cdot { x }^{ 15 } } [/tex]
[tex]\frac { 1 }{ 216\cdot { x }^{ 15 } } [/tex]
So the answer is :
[tex]\boxed { \frac { 1 }{ 216{ x }^{ 15 } } } [/tex]
(If the works are not readable there is an attachment where you can see the works better)