SAT Question a4bd60a3: Right Triangles And Trigonometry answer and explanation with Desmos solution

An equilateral triangle is a triangle in which all three sides have the same length and all three angles have a measure of $60^{\circ }$. The height of the triangle, $k\sqrt{3}$, is the length of the altitude from one vertex. The altitude divides the equilateral triangle into two congruent 30-60-90 right triangles, where the altitude is the side across from the $60^{\circ }$ angle in each 30-60-90 right triangle. Since the altitude has a length of $k\sqrt{3}$, it follows from the properties of 30-60-90 right triangles that the side across from each $30^{\circ }$ angle has a length of $k$ and each hypotenuse has a length of $2k$. In this case, the hypotenuse of each 30-60-90 right triangle is a side of the equilateral triangle; therefore, each side length of the equilateral triangle is $2k$. The perimeter of a triangle is the sum of the lengths of each side. It's given that the perimeter of the equilateral triangle is $624$; therefore, $2k+2k+2k=624$, or $6k=624$. Dividing both sides of this equation by $6$ yields $k=104$.