Someone help me quick

Write the symbol for every chemical element that has atomic number greater than 3 and atomic mass less than 12.0 u.

Use the periodic table to determine the electron configuration of dysprosium (dy) and americium (am) in noble-gas notation.

In a laboratory, 1.55mg of an organic compound containing carbon, hydrogen, and oxygen is burned for analysis. this combustion resulted in the formation of 1.45mg of carbon dioxide and .89 mg of water. what is the empirical formula for this compound?