Before working on the answer, let us define some things:
[tex]\begin{gathered} \sigma=1.3 \\ n=4000 \end{gathered}[/tex]Besides, we need to calculate the average (x bar) of roaches produced by a single roach in the week:
[tex]\bar{x}=\frac{15400}{4000}=3.85[/tex]Let's look at our z-score table. the value associated with a confidence level of 90% is
[tex]z^{}=1.645[/tex]Having calculated these things, we're done; for the desired confidence interval is given by
[tex]CI=(\bar{x}-z\cdot\frac{\sigma}{\sqrt[]{n}},\bar{x}+z\cdot\frac{\sigma}{\sqrt[]{n}})[/tex]Replacing the values we just got:
[tex]CI=(3.85-(1.645)\cdot\frac{1.3}{\sqrt[]{4000}},3.85+(1.645)\cdot\frac{1.3}{\sqrt[]{4000}})\ldots[/tex][tex]\ldots\approx(3.85-0.0338,3.85+0.0338)=(3.816,3.884)[/tex]The answer is
[tex](3.816,3.884)[/tex]