I'm pretty sure the 3rd one is right, use a calculator
I think it is d I think not sure tho
All of the above. it is a three dimensional pyramid, and a "polyhedron" means it is triangular.

Actually Welcome to the Concept of the Equilateral Triangles.
Since, we know that, all the sides of a triangle are equal, hence it is a Equilateral triangle.
Equilateral triangle has one all angles equal to 60°.
so, major angle P = 60°
hence, 2x=60°
===> x = 30°
Answer:
8x - 20
Step-by-step explanation:
6(2x - 3) - 2(2x + 1)
Distribute
6(2x) -6( 3) - 2(2x) -2( 1)
12x -18 -4x -2
Combine like terms
12x -4x -18 -2
8x-20