you should calculate( the area of a circle of radius 15 cm ) minus the area of the circle of radius (15 cm - width of the frame). I am not able to read the number, sorry.
That is the surface area of the frame.
Then, if area of circle radius is 100%, the % of face of the clock is:
(100xareaCircle(15cm-widthframe))/areaCircle15cm
