How does the earth's crust affect things that happen on and in the earth (such as earthquakes, volcanos, etc.)

during earthquakes and giant cracks are produced by the pressure of the moving rock. earthquakes and volcanoes occur along the edges of the plates. ... When plates move apart, they produce new ocean floor as magma from the mantle rises through volcanoes and deposits new rock along the plate boundaries.

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