To find the measure of the reflex angle \( j \), we first need to understand what a reflex angle is. A reflex angle is an angle that is greater than 180 degrees and less than 360 degrees.
If we have an angle of 120 degrees, the reflex angle corresponding to this can be found by subtracting the given angle from 360 degrees.
So, the calculation is:
\[ j = 360^\circ - 120^\circ \] \[ j = 240^\circ \]
Thus, the measure of the reflex angle \( j \) is 240 degrees.