What is the exact angle measure in radians?
This is more than a complete circle....a complete circle is 2pi radians (or 360 degrees)...so you need a fraction that is greater than 2pi
SO first and third options are no good.
Now as a ratio
420 is to 360 as ? is to 2 pi or:
420/360 = ? / 2pi
420/360 x 2pi = ? = 840pi /360 = 7/3 pi