Using undiluted D-76 in, one increases the development time 10 to 15% for every 4 sheets of 4x5 developed to account for the weakening of the developer.
One qt of straight D-76 can develop 16 sheets of 4x5. Say the dev. time is 10 minutes. Dev the first 4 at 10 minutes, dev the second 4 at 11 to 11.5 minutes, the third four at around 12 to 13 minutes. The last set of four 4x5's develop for 14 minutes or so. Then toss out the D-76.