#### Answer

The length of the tree frog is 65 millimeters.

#### Work Step by Step

The tree frog was 6.5 cm long.
To find the length of the frog measured in millimeters, we need to multiply 6.5 by the ratio that converts centimeters to millimeters.
The ratio that converts centimeters to millimeters is $\frac{10\ millimeters}{1\ centimeter}$
So: 6.5 centimeters $\times$ $\frac{10\ millimeters}{1\ centimeter}$
= 6.5 $\times$ 10
= 65 millimeters