To find the greatest common factor or GCF, first factor 12 and 30 and find factors that are both present in both numbers. 12 = 2*2*3 30 = 2*3*5 Both have a common factor of 2*3 which is 6, and since it is present in both numbers and is the greatest, it is the GCF. The GCF of 12 and 30 is 6. Hope this helps.
d is wrong because 12 cannot be divided by 30. a and b are wrong because the question is looking for the greatest meaning the highest number, not the least.
