title: Calculate angle to translate the circle at the 90 degree on an arc
body: <p>I have one design like this:<a href="https://i.stack.imgur.com/gAGkM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/gAGkM.png" alt="enter image description here"></a></p>
  
  <p>Now i want to calculate angle between the clicked circle and the position at 90 degrees on outer arc. How do i calculate that ?</p>
  
  <p>I have angle of outer circles in radians.</p>