A short peptide on complete hydrolysis produces 3 moles of glycine...

Peptide linkage is also known as peptide bond. It is an amide formed between $- COOHand - {NH}_{2}$ group by elimination of a water molecule. It is represented as
$- CO - NH -$.

Number of peptide linkages $= ($Total amino acids $- 1 )$

Now, given that short peptide on hydrolysis give seven amino acids.
$= 7 - 1 = 6$