We are told tha our sample consists of n=1100 polls, out if which 542 said yes.
The 90% confidence level is not used to calculate the point estimate of the population proportion p.
The best point estimate of the population proportion p is obtained by simply calculating the the proportion among the sample. That is
[tex]p^{\prime}=\frac{x}{n}=\frac{542}{1100}=0.492727272[/tex]which rounded to three decimal places is
[tex]p^{\prime}\approx0.493[/tex]