we are given the reaction Cu + 2AgNO3 ---> Cu(NO3)2 + 2Ag. This means for every mole Cu used, there are 2 moles of Ag produced. In this case, given 31.75 g Cu, converting to moles through molar mass and using stoichiometric ratio and the molar mass of Ag, the mass Ag produced is 107.9 grams.
Try this link https://chem.libretexts.org/Courses/Mount_Aloysius_College/CHEM_100%3A_General_Chemistry_(O'Connor)/08%3A_Solids_Liquids_and_Gases/8.E%3A_Solids_Liquids_and_Gases_(Exercises)