To solve for the missing measure in an enlargement of a triangle, you need to establish a proportion based on the corresponding sides of the triangles.
In this case, the smaller triangle has side lengths of 9 millimeters and 6 millimeters, while the larger triangle has corresponding side lengths denoted as \( x \) millimeters and 16 millimeters.
When setting up a proportion to solve for \( x \), you must ensure that corresponding parts are placed in the same position. For example, you could set up the proportion as follows:
\[ \frac{9 \text{ mm}}{x \text{ mm}} = \frac{6 \text{ mm}}{16 \text{ mm}} \]
This shows that the sides of the triangles are proportional because they correspond correctly (9 mm corresponds to \( x \), and 6 mm corresponds to 16 mm).
Thus, the correct statement about setting up a proportion to solve for the missing measure is:
Corresponding parts must be in the same position.