Answer
$6.45\text{ mm}$.
Increases if the largest measurement is doubled.
Work Step by Step
The range has the same units of measure as the data items in the sample (millimetres, or $mm$).
It is computed as the difference of the largest and smallest data item:
$$19.7-13.25=6.45\text{ mm}$$
Note: the result can be obtained by invoking the "Descriptive Statistics" option of our Data Analysis feature to obtain a summary shown below in the attached screen snippet.
If we doubled the largest measurement, the range would be
$$\begin{align*}
(19.7+19.7)-13.25& =(19.7+6.45)\text{ mm}& & \\
& =26.15 \text{ mm} \end{align*}$$
That is, it would increase.
