Answer: a = 100
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Step-by-step explanation:
There are n = 7 sides to this polygon (so it's a heptagon)
The interior angles add up to 180(n-2) = 180*(7-2) = 900 degrees.
So that means,
69+284+62+62+242+81+a = 900
800+a = 900
a = 900-800
a = 100