The enzyme rnase a requires the formation of four disulphide bonds amongst its eight cysteine residues. if this is entirely a random phenomenon, the probability

The enzyme RNase A requires the formation of four disulphide bonds amongst its eight cysteine residues. If this is entirely a random phenomenon, the probability that the first correct disulphide bond will be formed is 1/7. Following the same logic, what is the probability of formation of all four correct disulphide bonds?