List two characteristicts that fern, club mosses, and horse tails share

Write a paragraph that provides examples of each stage of volcanic activity, a description of the volcano, and facts about each stage.

Can someone me with questions 12 and 13 plz.

Write the empirical chemical formula of calcium with a mass percent of 38.8, phosphorus with a mass percent of 20.0, and oxygen with a mass percent of 41.3.