Assuming you do not know the location of the start codon how

Assuming you do not know the location of the start codon, how many possible reading frames are there in a mRNA?

As we know our genetic code is triplet and made up of 4 bases and there will be 64 combinations of codons.among that start codon is AUG, it may repeat twice .As mRNA ORF will start with start codon, there may be two open reading frames possible in mRNA.