#### Answer

$ (2a-9b)(2a+9b)$

#### Work Step by Step

The given expression can be written as:
$=(2a)^2-(9b)^2$
RECALL:
A difference of two squares can be factored using the formula:
$x^2-y^2=(x-y)(x+y)$
Use the formula above with $x=2a$ and $y=9b$ to obtain:
$= (2a-9b)(2a+9b)$