Explanation

(c) Let $a_{1}$ and $a_{2}$ be amplitudes of the two waves.
For maximum intensity
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ I_{\max} = \left( a_{1} + a_{2} \right)^{2}$
For minimum intensity
$\ \ \ \ \ \ \ \ \ \ \ \ \ I_{\min} = \left( a_{1} - a_{2} \right)^{2}$
Given, $\frac{I_{max}}{I_{\min}} = \frac{25}{1} = \frac{\left( a_{1} + a_{2} \right)^{2}}{\left( a_{1} - a_{2} \right)^{2}}$
$\Rightarrow \ \frac{a_{1} + a_{2}}{a_{1} - a_{2}} = \frac{5}{1}$
$\Rightarrow \ \ \ \ \ \ \ \ \ \ \ \frac{a_{1}}{a_{2}} = \frac{3}{2}$
(law of componendo and dividendo)
Also, $Intensity\ \propto (amplitude)^{2}$
$\therefore\frac{I_{1}}{I_{2}} = \left( \frac{a_{1}}{a_{2}} \right)^{2} = \frac{9}{4}$