Answer:
The minimum number of subjects needed is 385.
Step-by-step explanation:
In a sample with a number n of people surveyed with a probability of a success of
, and a confidence level of
, we have the following confidence interval of proportions.
In which
z is the z-score that has a p-value of
.
The margin of error is:

95% confidence level
So
, z is the value of Z that has a p-value of
, so
.
95% confidence, within 5 percentage points, and a previous estimate is not known.
The sample size is n for which M = 0.05. We don't know the true proportion, so we use 
Then






Rounding up:
The minimum number of subjects needed is 385.