Can someone help me to answer this correctly, please, and explain it. Please answer these 2 questions, I don't have more money to buy more questions. These 2 questions are different.

1. a.

1. b.

If a sample of silver contains 1.48104 atoms of silver-107 and 1.38104 atoms of silver-109, what is the percentage of silver-107 atoms in the sample? % The element lanthanum has an atomic weight of 139 and consists of two stable isotopes lanthanum-138 and lanthanum-139. The isotope lanthanum-138 has a mass of 138 amu and a percent natural abundance of 8.90102%. The isotope lanthanum-139 has a percent natural abundance of 99.9%. What is the mass of lanthanum-139? amu