I found the exercise on the internet and attached is the image of the DNA strand mentioned in the question.
Between each Thymine - Adenine bond there are two hydrogen bonds, while in each Guanine - Cytosine bond there are three hydrogen bonds. This is important because allows each base to connect only with that that is the correspondent.
So, the number hydrogen bonds that exist between DNAs dna strand and its complementary strand is 19.
2bonds×2 (1 Adenine + 1 Thymine) + 3bonds×5 (2 guanines + 3 cytosines) = 19 bonds
