The EPA considers indoor radon levels above 4 picocuries per liter (pCi/L) of air to be high enough to warrant amelioration efforts. We want to compute the 95% confidence interval of the proportion of all the households in the county that don't meet the EPA guidelines and we want to make sure that our margin of error is within 5 percentage points. How many households do we need to test to guarantee such margin of error?

Please include step-by-step explanation and use commands qnorm and/or qt in R to compute the numerical solution. Thank you!