To find the arc measure of \( MN \), we can use the properties of inscribed angles.
Since triangle \( LMN \) is inscribed in the circle and has diameter \( LM \), we know that angle \( N \) will be a right angle (90°) because any angle inscribed in a semicircle is a right angle.
Using the information given:
- Measure of angle \( L = 37° \).
- Therefore, measure of angle \( N \) is \( 90° \).
The sum of the angles in triangle \( LMN \) is \( 180° \): \[ \text{angle } L + \text{angle } M + \text{angle } N = 180° \] Substituting the known angles: \[ 37° + \text{angle } M + 90° = 180° \] \[ \text{angle } M = 180° - 127° = 53° \]
Now, to find the arc \( MN \). The measure of arc \( MN \) is given by twice the measure of the inscribed angle \( M \) that subtends it: \[ \text{Arc } MN = 2 \times \text{angle } M = 2 \times 53° = 106°. \]
Therefore, the arc measure of \( MN \) is \( \boxed{106°} \).