Provide the setup and the answer of the question provided below. Lithium has two isotopes. 6Li has an abundance of 7.42% and has a mass of 6.01 amu. If another isotpe, 7Li, has an abundance of 92.58% and a mass of 7.02 amu, please calculate the atomic mass of lithium. (Keep two digits after decimal in your answer)

Which best describes the present-day universe? opaque, expanding very slowly, stars produce heavy elements transparent, expanding at an accelerated rate, stars produce heavy elements opaque, expanding at an accelerated rate, stars produce only hydrogen and helium transparent, expanding very slowly, stars produce only hydrogen and helium