Final answer:
The measure of angle JKM in the triangle is 119 degrees, calculated by using the external angle theorem and the sum of angles in a triangle.
Step-by-step explanation:
To find $m\angle JKM$ in triangle JKL with the given information, we will use the fact that the sum of the angles in a triangle is 180 degrees. Angle J is given as $x$ degrees, angle L is 58 degrees, and the external angle JKM is given as $2x - 3$ degrees.
Since $\angle JKM$ is an external angle to triangle JKL, it equals the sum of the two non-adjacent internal angles, J and L. Therefore:
$2x - 3 = x + 58$
Now, we can solve for $x$:
$x = 61$ degrees
Finally, we substitute $x$ back into the expression for $\angle JKM$ to find the measure of that angle:
$m\angle JKM = 2(61) - 3$
$m\angle JKM = 119$ degrees