To specify three amino acids, a total of three codons are needed. Each codon, which is a sequence of three nucleotides in mRNA, codes for a specific amino acid. Therefore, one codon is required for each amino acid.
For example, if the sequence of codons is AUG (methionine), UUU (phenylalanine), and GCA (alanine), then these three codons will specify the three amino acids: methionine, phenylalanine, and alanine.
In summary, the number of codons needed to specify amino acids is equal to the number of amino acids. So, for three amino acids, three codons are required.