Answer:
Purple colour arises due to the dominant alleles whereas white colour arises due to the recessive alleles. 
For the purple colour to arise, even one of the dominant allele will be enough to cause the effect. On the other hand to see the recessive white trait, both the alleles of the gene should be recessive.
To ensure that only white flowers are grown, the farmers need to cross both white flowered plants to get the desired result. 
 
        
             
        
        
        
The answer is limiting factors. 
I hope this helped you!
        
                    
             
        
        
        
Hey there!!
For box X, the allele would have to be bc to match the data you have here.
I really hope this helps!!