Answer
$\frac{I_p}{I_{cen}} = 0.336$
Work Step by Step
In part (a), we found that the amplitude of the electric field at point P is $~~2.32~\mu V/m$
The amplitude of the resultant electric field at the center is $~~4.00~\mu V/m$
$I_p \propto (2.32~\mu V/m)^2$
$I_{cen} \propto (4.00~\mu V/m)^2$
$\frac{I_p}{I_{cen}} = \frac{(2.32)^2}{(4.00)^2} = 0.336$
