Hey there
Thats easy
Precipitation occurs when cations and anions in aqueous solution combine to form an insoluble ionic compound called precipitation. So, you can refer to a solubility chart or draw polar/nonpolar lewis structures, that might be helpful.
Remember water is polar so polar molecules will dissolve in water 
        
             
        
        
        
Answer:
the highest is "A" and the lower is "C"
 
        
             
        
        
        
The answer is na3po4+3koh=3naoh+k3po4