Anyone know this please help

This is very simple!!! Your 'stuckness' will disappear in a minute.

∠AOB = ∠COB = 90º

1st      Find an angle  AOC          ∠AOC = ∠AOB + ∠COB

                                                     ∠AOC = 2[arccos( AO / OB )] = 108.6293306º

2nd     Find the central angle of a major arc ADC

                 That angle is    360º - ∠AOC = 251.3706694º

3rd       Find the length of ADC

                                         ADC = 2 * 7 * pi * ( 251.3706694 / 360 ) = 30.711

1/2 of the angle at O     arcos (7/12) = 54.31^o

    so O is 108.6 ^o

        the arc you are looking for is   360 - 108.6 = 251.37^o

^{Pi (2*7)  x   251.37/360 = .....}