How can valence electrons be used to predict the type of compounds formed?

Valence electrons are the electrons in the outermost shell. Those are the electrons on an atom that can be gained or lost in a chemical reaction.
Elements that are left on the periodic table  have relatively few valence electrons, and can form ions  more easily by losing their valence electrons to form positively charged cations.
Nonmetals are further to the right on the periodic table, so they gain electrons relatively easily and lose them with difficulty. 

Since there is the same amount of agn03 in both silver chloride and silver nitrate they produce the same amount of moles. therefore silver chloride produces the same amount of silver nitrate, so your answer is 15.0 moles of silver nitrate. i hope this !