$.$ Ashortpeptidemadeupentirelyoftheaminoacidalaninehasamolecularweight of $231\mathrm{.}26$ amu. Alanine is made of up C$,$ N$,$ H$,$ and O$.$ The percent composition by mass of carbon and nitrogen in the peptide are as follows:

C $=46\mathrm{.}75\%,$ N $=18\mathrm{.}17\%$

All of the oxygen from an $800$ mg sample of the peptide is removed and converted into water. The water produced weighed $249\mathrm{.}4$ mg$.$ Calculate the molecular formula of this short peptide. If each alanine molecule contains $3$ carbons, how many alanine residues are present in the short peptide?