Muhammed was the prophet that founded Islam, according to his teachings he was sent to confirm the monotheist idea and religion of Adam, Abraham, Moses and Jesus, he mainly confirmed the Jewish religion, and the catholic religion but treated jesus and others as prophets. He was born in what we know today as Saudi Arabia.
Marginal costs. Keep in mind that marginal means on the edge of something, so the cost of producing one more unit would be on the edge. Hope this explanation helps.
