A circular pizza has a angle of 360 degrees. When you cut it into 3 equal pieces you divide 360 by 3,you get 120 degrees. And following the conversion of 120 degree into radian you get 2pie/3 radians.
Positive charge you gave the lines pointing away, negative charge is pointing toward. Don’t have a photo so I can’t fill in the blanks BUT I can tell you the logic