Here it is
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Amino acids linked together by amide linkages to make a peptide bond.
A tetrapeptide means there are four amino acids and three peptide linkages.
By convention the amino acid residue with the free amino group is called the N- terminal lies to left and free carboxylic group on the C-terminal appears on the right.
In our question alanine is on the left with is N-terminal residue and   either serine or valine are on the right end with their free carboxylic ends.Glycine is a achiral amino acid so is going to be in between N terminus and the C terminus.
Different combinations which are feasible
Alanine -glycine- valine-serine
Alanine -valine-glycine-serine
Alanine-glycine-serine  -valine
Alanine-serine-glycine -valine