To find the measure of the exterior angle \( x \) of a triangle, we can use the fact that the sum of the exterior angle is equal to the sum of the two non-adjacent interior angles.
Given the interior angles of the triangle are \( 37^\circ \) and \( 42^\circ \), we can find \( x \) using the formula:
\[ x = \text{(sum of the two non-adjacent interior angles)} \]
Calculating the sum of the two given angles:
\[ x = 37^\circ + 42^\circ \]
Now, adding these together gives:
\[ x = 79^\circ \]
Thus, the measure of the exterior angle \( x \) is:
\[ \boxed{79^\circ} \]