Three identical square sheets of paper each with side length $10$ 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.

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 $a+b+c$?