Suppose a sampling plan designed to screen product lots requires a burn-in done on 300 pieces for 168 hours, with no more than 1 fail allowed for the lot to be accepted. Assuming a 60% con?dence level, how many hours of burn-in are needed to get the same level of protection if we switch to only accepting lots with zero fails? How many units must we burn-in if we shorten the time to 48 hours, keep 60% con?dence, with zero fails allowed and the same level of failure rate protection?