How many different amino acids could theoretically be encoded by nucleic acids containing four different nucleotides if

Question:

How many different amino acids could theoretically be encoded by nucleic acids containing four different nucleotides if
(a) Each nucleotide coded for one amino acid;
(b) Consecutive sequences of two nucleotides coded for one amino acid;
(c) Consecutive sequences of three nucleotides coded for one amino acid;
(d) Consecutive sequences of four nucleotides coded for one amino acid?