FB of line BA is BB of line AB. The relation b/w FB and BB of a line is given as; BB = FB ± 180° If FB > 180° then use minus sign If FB ≤ 180° then use plus sign Given that FB of AB = 40° 15’ i.e. less than 180°. So, we will use plus sign. BB of AB = FB of BA = FB of AB + 180° = 40° 15’ + 180° ∴ FB of BA = 220° 15’