#### Answer

x = 21

#### Work Step by Step

$\frac{3}{7}$ = $\frac{9}{x}$
First, use the Cross Products Property.
3x = 7(9)
Simplify the right side of the equation.
3x = 63
To find x, divide both sides of the equation by 3.
$\frac{3x}{3}$ = $\frac{63}{3}$
x = 21