In eukaryotes, the first amino acid in a growing polypeptide chain is always because the only codon for this amino acid is also the codon. This amino acid is not always the first amino acid in a processed protein because of

1. Methionine

2. Start codon

3. Proteolysis

Explanation:

The process of translation begins when the codons are read by the tRNA molecule which with anticodon loop identifies the codon and then brings the specific amino acid corresponding the codon.

The translation begins when a specific nucleotide sequence 'AUG' called start codon is read by the tRNA. The AUG codon code for Methionine amino acid therefore in a growing polypeptide methionine is present but post-translational modification called proteolysis can remove the methionine amino acid.

Thus, Methionine, Start codon and Proteolysis are correct.

69 is the correct math for the amino acids