#### Answer

(3n+20)(3n-20)

#### Work Step by Step

We use the formula for the difference of squares to apply to this question.
The difference of squares formula is:
$(a-b) (a+b) = a^{2} - b^{2}$
= $9n^{2}$ - 400
*** Take the square root of $9n^{2}$ which is 3n. Becuase 3n × 3n= $9n^{2}$
*** Take the square root of 400 which is 20. Becuase 20 × 20= 400
= $(3n)^{2}−20^{2}$
In the given formula let 3n represents a and 20 represents b.
$(3n)^{2}−20^{2}$ = (3n+20)(3n-20)