I can do it using trigonometry.
Draw a line from O to the point where the circle touches the base line. This will be at right angles to EF and will have length 40. Then draw a line from A parallel to the base to meet OG at H.
consider triangle OAH:-
side OH = 40-25 = 15 cm
cos < AOH = 15/40 giving m < AOH = 67.976 degrees
So m < AOB = 67.976 * 2 = 135.95 degrees
in radians this is 2.37 radians (answer)
Part B:-
