The average molar mass of lithium is 6.941. A sample of lithium consists of two isotopes with masses of 6.01512 amu and 7.01600 amu. Determine the percent abundance of each isotope.
a) 74.9% Li-6 and 92.51% Li-7
b) 8.45% Li-6 and 91.55% Li-7
c) 12.49% Li-6 and 87.51% Li-7
d) 91.55% Li-6 and 8.45% Li-7
e) 92.51% Li-6 and 7.49% Li-7