AMC 10 2021-fall-b Problem 18

Three identical square sheets of paper each with side length $6{ }$ are stacked on top of each other. The middle sheet is rotated clockwise $30^\circ$ about its center and the top sheet is rotated clockwise $60^\circ$ about its center, resulting in the $24$-sided polygon shown in the figure below. The area of this polygon can be expressed in the form $a-b\sqrt{c}$, where $a$, $b$, and $c$ are positive integers, and $c$ is not divisible by the square of any prime. What is $a+b+c?$

$(\textbf{A})\: 75 (\textbf{B}) \: 93 (\textbf{C}) \: 96 (\textbf{D}) \: 129 (\textbf{E}) \: 147$