Complement of an angle = 90° - x.
Supplement of the complement of an angle = 180 - (90 - x).
= 180 - 90 + x
= 90 + x
Supplement of the complement of an angle less the complement of an angle = (90 + x) - (90 - x)
= 90 + x - 90 + x
= 2x
Now, the quotient of the supplement of the angle and the number 3 is
.
It is given that supplement of the complement of an angle less the complement of an angle exceeds the quotient of the supplement of the angle and the number 3 by 73.
Therefore, 2x = 

Multiply both sides by 3.
6x = 180 - x + 219
= 399 - x
Add x to both sides.
6x + x = 399
7x = 399
Divide both sides by 7.
x = 57
Hence, the required angle = 57°.
Step-by-step explanation:
arithmetic sequence.
an = an-1 + c = a1 + (n-1)c
c is in our case 2 (every new shape has 2 more vertices).
we have a a1 = 3.
an = 3 + 2(n-1)
so,
a21 = 3 + 2(20) = 3 + 40 = 43
the 21st shadow will have 43 vertices.