What is a difference of squares with a factor of (3x + 7) ?

9x² - 49

Step-by-step explanation:

A difference of squares factors in general as

a² - b² = (a + b) (a - b)

Given (3x + 7) with a = 3x and b = 7

Then the other factor is (3x - 7)

(3x + 7) (3x - 7)

= (3x) ² - 7²

= 9x² - 49