My study team is at odds with the answer to this question, particularly (b) and (c).
Input highly appreciated.

(a) What are the phases present and what are the compositions of the phases in an alloy of 90 wt% Silver in Copper at 780degC?
(b) Is it possible to liquefy this alloy without raising the temprature abpve 780degC simply by adding more silver to it? If so, how much silver would you have to add to 10Kg of alloy to make it 100% liquid?
(c) Is it possible to liquefy this alloy at 780degC by adding more copper to it? If so, how much copper would you have to add to 10Kg of alloy to make it 100% Liquid?