Thank you for answering this question.
Note the rules
[tex]\\ \rm\Rrightarrow \dfrac{7^{12}7^9}{(7^6)^3}[/tex]
[tex]\\ \rm\Rrightarrow \dfrac{7^{21}}{7^{18}}[/tex]
[tex]\\ \rm\Rrightarrow 7^3[/tex]
[tex]\\ \rm\Rrightarrow 729[/tex]