b) 3n .( 1/9) ^4 = 27.

b) 3ⁿ . ${\left(\frac{1}{9}\right)}^4$= 27

3ⁿ = 3³ : ${\left(\frac{1}{3}\right)}^8$

3ⁿ = 3³ . 3⁸

3ⁿ = 3¹¹

n = 11

Vậy n = 11.