The correct answer here is that the sum has to be 84. This is due to the fact that 30 + 54 is 84, and the greatest common factor is 6 because the factors of 30 are 1, 2, 3, 5, 6 , 10, 15, and 54's Factors: 1, 2, 3, 6, 9, 18, 27, and 54, so from this we can see that 6 is the great common factor.