Call the center point X.
Quadrilateral AEXD has a total angle sum of 360 degrees.
Since XEA and XDA is 90 degrees, and angle A is 60 degrees.
This means that angle EXD is 90 + 90 + 60 + x = 360
240 + x = 360
x = 120
So angle EXD is 120 degrees.
Based on supplements, EXB is 60 degrees.
Triangles EXB and DXC are 30 60 90 triangles.
Can you find angles XBC and XCB?
Hint: you might need two variables and make a system of equations