The diagram in the question is missing has been attached.
Answer: The first three nucleotide of the complementary DNA strand will be GGC.
DNA contains nucleotide pairs on a sugar phosphate backbone. The nucleotide pairs are connected by hydrogen bonds and each nucleotide pairs with only one other nucleotide. The bases are of two types: purine and pyrimidine. The purine bases bond only to pyrimidine bases. The base pairing follows Chargaff’s rule where adenine forms a pair with thymine by two hydrogen bonds and Guanine forms a bond with cytosine with three hydrogen bonds between them .