(1/3)^(n-7)=3^(6n-9)

(3^(-1))^(n-7) = 3^(6n-9)

3^((-1)(n-7)) = 3^(6n-9)

3^(7-n) = 3^(6n-9) multiply both sides by (3^(6n-9))^(-1)

(3^(7-n)) *(3^(6n-9))^(-1) = 1

(3^(7-n)) *(3^((-1)*(6n-9))) = 1

3^((7-n) + ((-1)(6n-9)) = 3^0

(7-n) - (6n-9) = 3^0

7 - n - 6n + 9 = 3^0

-7n + 16 = 3^0

7n = 16

n = 16/7