first off, next time make sure your screenshot is sharp enough and clear enough.
so if we notice the two points on the midline that you took, the horizontal distance will be from -4.5 to 3.6 which gives us a distance over the x-axis of 8.1 units, now half of that will be to the "orange" area, half of 8.1 is 4.05. Now, the ending of the "orange" part is not really clear, but that'd be the period, because that is the part that's repeating.
How long is it?
well, our 4.05 half ends after the "2", so without a better calibration of the picture, hmmm 2.20 or thereabouts, let's make an assumption the "orange" section ends at 16, so that'd be 4.05 + (16 - 2) ≈ 18.05.