How to calculate what pie of a pie chart matches a specific (x,y) coordinate

[MagicNRS]

Please find below a pie chart with a green cross (example of a specific x,y-coordinate).
The pie chart does have different sized parts.
Question: how to calculate (in Excel) what part of the pie matches the coordinates?

 

[lev888]

x,y is cartesian coordinates. Angle + radius is polar coordinates. Look up how to convert one into the other. Given the angle, you can find which of the parts contains the point.

 

[MagicNRS]

Thanks. After your to the point ‘teaser’ I found that Excel has a built-in ATAN2 function and a circle degree converter. Thanks for bringing me up to speed.