For the first one, let's assume that you have indeed selected "Overall Mean" as requested. (I don't know whether the button with dark blue or the one with white background is selected.) Then the length of the dotted line is the difference between the mean value (vertical line in the middle) and the data point.
IF the first point corresponded to A = 36.72 (?! that doesn't look likely: see "however" below ...)
and the mean is M = 37.05 (that looks OK, for the vertical line),
then the length of the said dotted line WOULD be M - A = 37.05 - 36.72 = 0.33.
HOWEVER, according to the "Age" scale at the bottom of the first frame, it looks as if the upmost shown data point is rather around X1 = 25... I guess that "A" might rather be the first group mean.
I think you can select that first data point in order to see the exact value, and/or maybe use a different frame (the "calculations" frame? maybe scroll down and/or use the "Show data" button?) to see the exact value of that first data point (which should be around X1 = 25, maybe slightly less? and it should come just before the second value of ~ 49). With a value of about X1 = 25... you should get for the length (= difference) something around
M - X1 = 37... - 25... = 12...)
Then it will work the same way with "group mean" selected. The instruction says "select group means" and I don't know what would display for the "first dotted line", so I cannot give an answer for sure with the information you give. I think there are 2 possibilities: (1) It might still be the same data, but now several vertical lines for the different "Group means" A = 36.72, B = 37.60, etc.
In that case, the length of the fist dotted line should be A - X1 = 36.72 - 25... = 11....
Or (2): It might display the group means A, B, C ... with a dotted line towards the overall mean. In that case the first dotted line would be M - A = 37.05 - 36.72 = 0.33.
For the second screen capture, the first dotted line appears to be between X1 = 5.9... (Again, select that point or click "Show data" to see the exact value -- according to the scale it looks definitely larger than "Rural = 5.67") and the mean M = 6.39. So the lenth of the first dotted line should be something around M - X1 = 6.39 - 5.9... = 0.4...
Similar for the group mean, with M = 6.39 (?) replaced by Rural = 5.67. (Depending on what you see, it should be either X1 - Rural, or M - Rural = 0.72.
Let me know if you can't figure it out with these instructions, but with the information given on the two screenshots only, it's not possible to give a better answer.
