An environmental agency worries that many cars may be violating

An environmental agency worries that many cars may be violating clean air emissions standards. The agency hopes to check a sample of vehicles in order to estimate that percentage with a margin of error of 6% and 95% confidence. To gauge the size of the problem, the agency first picks 40 cars and finds 6 with faulty emissions systems. How many should be sampled for a full investigation?

The environmental agency should sample at least ____vehicles? (round to the nearest whole number)