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xchynax
because all angles in a triangle add up to 180° 100°+30°=130° 180°-130°=50°

I hope this is helpful and correct♡♡~~Chyna
answer: a. 50°
work: all the angles add up to 180°. first, you see how much you have already. 100° + 30° = 130°. next, you do 180° - 130° = 50° because you have to subtract to see what the measurement of A.