â acb = 8°
step-by-step explanation:
â xba lies on the circle and is half the measure of the intercepted arc ax
hence
measure of arc ax = 2 à 42° = 84°
â acb is outside the circle and is
â acb = (arcab - arcax ), hence
â acb = 0.5 (100 - 84) = 0.5 Ă 16° = 8°