Lithium has only two naturally occurring isotopes: lithium-6 and lithium-7. Lithium -6 has a mass of 6.01512 and makes up 7.42 percent of all...

1. Lithium has only two naturally occurring isotopes: lithium-6 and lithium-7. Lithium -6 has a mass of 6.01512 and makes up 7.42 percent of all naturally occurring lithium. Lithium -7 has a mass of 7.016 and makes up the remaining 92.58 percent. What is the atomic mass of lithium? (Show your calculations)