Answer
See below.
Work Step by Step
The margin of error of a sample size $n$ is a $95\%$ probability that a sample lies within the margin of error which is $\pm\frac{1}{\sqrt n}\cdot 100\%$
a) Hence here the margin of error: $\pm\frac{1}{\sqrt {814}}\cdot 100\%\approx\pm3.5\%$
b) Thus we can be $95\% $confident that between $69-3.5=65.5\%$ and $69+3.5=72.5\%$ of the population favor required gun registration
as a means to reduce gun violence.
