Hello,
I suppose as we don't see correctely the 2nd image, that it is the first one.
Angles DOY and DKY intersept then same arc are equals.
5x+15=3x+21
==>2x=6
==>x=3 and 5x+15=5*3+15=30°, 3x+21=3*3+21=30°
Angle OYK=15x=15*3=45°
Angle ODK=9x+18=9*3+18=45° =Angle OYK which intersept the same arc.