Function making of certai block

hello can some one plz tell me how to make a matlab function of this

ProbSuccess(ProbSuc,ProbPosSuc,ProbPosFail,NPos,NNeg)

where ProbSuc = P(Success).

ProbPosSuc = P(For | Success).

ProbPosFail = P(For | Fail).

NPos = the number of reviewers who have given a positive review.

NNeg = the number of reviewers who have given a negative review.

This returns the conditional probability of success, given these parameters.