Sunlight is used in a double slit interference experiment. The fourth$-$order maximum for a wavelength of $490$ nm occurs at an angle of theta$=90$ degrees. Thus, it is on the verge of being eliminated from the pattern because theta cannot exceed $90$ degrees in Eq$.35-14.($a$)$ What least wavelength in the visible range $(400$ nm to $700$ nm$)$ are not present in the third order maxima? To eliminate all of the visible light in the fourth order maximum, $($b$)$ should the slit separation be increased or decreased and $($c$)$ what least change in separation is needed?