#### Answer

The print measures $13.5$ cm on its longer side.

#### Work Step by Step

We can set up a proportion that compares the dimensions of a negative to the dimensions of the print:
$\frac{3}{2} = \frac{x}{9}$
Use the cross products property to eliminate the fractions:
$2x = 27$
Divide each side by $2$ to solve for $x$:
$x = 13.5$ cm
The print measures $13.5$ cm on its longer side.