The overall charge of any compound is going to be zero. ag has a charge of +1 and co3 has a charge of -2. if we add the charges for only one of each ion together +1 + -2 = -1. but -1 cannot be the charge of the compound, so how many more ag+1 should we add to make the charge = 0? if we have 2 ag+1 and 1 co3-2, let’s add those charges together. +1 + +1 + -2 = 0. so we have to have two ag+1 and one co3-2 to make a compound. what does that look like?