I should have specified the area between.
Y bar and equation for the location of the centroid in the Y axis is writen in my question. All answers were fine and helpful. The inside area makes sense and makes a good assumption CPhill.
And how much posts have you all answered, if you had a question you could ask and simply wait for a reply or ask for terms such as y bar to be clarified. We are all at fault here but sarcasm ain't friendly.
I can understand it now from answers Cheers.
