X should be 7 after doing all the calculation.
Answer:
regular pentadecagon
Step-by-step explanation:
it has 15 sides
that is what matches the exterior angled sum property - 360degree
let me explain it
1 side = 180 - 156 = 24
360/24 = 15
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B= 30
a2+b2=c2
72^2+b^2 = 78^2
5184+b^2 = 6084
b2 = 900
b = 30
