The DNA fragment contains 120 guanyl nucleotides, which is 20% of the total

The DNA fragment contains 120 guanyl nucleotides, which is 20% of the total. Determine the amount of each nucleotide in the fragment, the length and mass of this DNA fragment.

The number of guanyl nucleotides is equal to the number of cytidyl nucleotides. The number of adenyl is equal to the number of thymidyl.
G = C = 120 n = 20%
100% – 20% – 20% = 60% / 2 = 30%
120 * 100/20 = 600 total nucleotides.
600 * 30/100 = 180 n
T = A = 180 n = 30%
DNA molecule length: 600 * 0.34 = 204 nm.
Molecular weight of the molecule: 600 * 345 = 207000 g / mol.