Explain the concept of sea floor spreading

Arational expression has been simplified below. (x-5) (x+1)/3(x+1) = x-5/3 for what values of x are the two expressions equal

The gene that causes sickle-cell disease is present in a higher percentage of residents of sub-saharan africa than among those of african descent living in the united states. even though this gene causes sickle-cell disease, it also provides some protection from malaria, a serious disease that is widespread in sub-saharan africa but absent in the united states. discuss an evolutionary process that could account for the different percentages of the sickle-cell gene among residents of the two regions.

What is earths lithospheric plates interact at