hcf (each stack) = hcf (1680,1056) . = Find the prime factorization of 1056 1056 = 2 × 2 × 2 × 2 × 2 × 3 × 11 Find the prime factorization of 1680 1680 = 2 × 2 × 2 × 2 × 3 × 5 × 7 To find the gcf, multiply all the prime factors common to both numbers: Therefore, GCF = 2 × 2 × 2 × 2 × 3 GCF = 48 no of stacks of maths book = 1680/48 = 35 no of stacks of science book = 1056/48 =22 total stacks= 35+22=57