Write out the equation: AgNO3(aq)+K2SO4(aq) --> Ag2SO4(s)+K2(NO3)...
Balance the equation: 2 AgNO3(aq)+K2SO4(aq) --> Ag2SO4(s)+K2(NO3)2...
Remember to keep molecules intact when you write out the ions. (2Ag+)+(2NO3-)+(2K+)+(SO42-) --> (Ag2SO42 Cancel out all the spectator ions. These are ions that watch the reaction that didn't change. For this problem 2K+ & 2NO3- are the spectator ions.
You are left with your net ionic equation of 2Ag+(aq)+SO42-(aq)-->Ag2SO4(s)