#### Answer

$4g^{2} - 81h^{2}$

#### Work Step by Step

We use the formula for the difference of squares to apply to this question.
The difference of squares formula is:
$(a-b) (a+b) = a^{2} - b^{2}$
In the given formula let 2g represents a and 9h represents b.
$(2g-9h) (2g+9h) = (2g)^{2} - (9h)^{2}$
= $4g^{2} - 81h^{2}$