A tetra-peptide is made of naturally occuring alanine serine glycine and valine.

It is given that $\mathrm{C}$-terminal amino acid is alanine and $\mathrm{N}$-terminal amino acid is chiral, thus glycine can't be $\mathrm{N}$-terminal amino acid as it is an achiral amino acid. Therefore possible sequence of tetra-peptide are as follows.

(i) Alanine, glycine, serine, valine

(ii) Alanine, glycine, valine, serine

(iii) Alanine, serine, glycine, valine

(iv) Alanine, valine, glycine, serine

Thus it can have $4$ possible sequences of the tetrapeptide.