4.2 what paces back and forth on the ocean floor?

As explained below.

Explanation:

The ocean is characterized by the horizontal and vertical motion of the plates in the back and forth motion of the plate boundary like in the high and low tides. With the seismic wave generated by the vertical motion of the seafloor. The seafloor configuration that includes the ocean topography and the water under is influenced by the shelf, slope, and rise. Also contained in the ocean floor include seamounts, volcanic islands, and the mid-oceanic ridges and rises. The mid-oceanic ridges thus create a revolutionary movement that recycles the earth's plates back and forth the zones and hence the is slabs are set back into motion on the deep ocean floor.

Ithink it should be 55.