The answer is; 3:1
This is derived by dividing the number of purple flowers with that of white flowers (or vice versa);
669/221 = 3.02714 which is approximately 3 (because we can only have whole plants). Based on this fact, it can be postulated that the Purple flower allele is dominant to that of white flower. (The purple flowers represent the Homozygous dominant and heterozygous population while the white flowers are the homozygous recessive population)