Why are most beds of sedimentary rock formed horizontally?

Sedimentary rocks formed in horizontal layers because sedimentary rocks are form when original sediments are get deposited sediments and the sentiments are sand, rock and mud. Due to action of the moving water and ice are get deposited more and less horizontally are due to the moving of water and ice. Sedimentary rocks are get deposited and contain the layers which are inclined outset then, it is also known as depositional dip.

the answer would be the third option, "no, ariel should have added 9^2 and 12^2 and compared that to 15^2."

this is found through the pythagorean theorem, which is a^2 + b^2 = c^2.

this is the correct way of solving the problem:

9^2 + 12^2 = 15^2

81 + 144 = 225

225 = 225