Calculate the remaining area of a quadrant with two non overlapping half circles

[p45cal]

I'm sorry P45cal but how did you arrive at this figure "4.583662361"?

Since the area has to be directly proportional to a linear value squared, I looked at the result obtained 'longhand' and divided it by any linear measurement squared, in this case I used the QuadrantRadius so in the case of 6 mtrs for your example case I did:
QuadrantRadius^2/QuadrantRemainingArea
becomes
6^2 /7.853981634
which is
36/7.853981634
which is
4.583662361

Another way to arrive at that value is to look at your longhand way of calculating and simplifying it over and over by rearranging it; I was too lazy to do that.