Answer:
im going to be honest i havent done this since las year and so i dont remember the value of that line outside but i think its 70*
Explanation:
reason is because the c is originally 180* but it has more of and angle so the angles obv increases and you can get the angle by multiplying 70*times 7x and divide by 3
i say 3 because of the amount of angles in a triangle and the line outside if i remember correctly is the "angles" of a triangle and that would be your answer