A researcher directs monochromatic laser light of wavelength \(\lambda\) through a pair of narrow identical slits onto a screen placed a distance \(L\) from the slits, where \(L \gg d\). The resulting intensity pattern on the screen consists of double-slit interference fringes modulated by a single-slit diffraction envelope. On the screen, the distance from the central maximum to the first minimum of the diffraction envelope is \(x\), and the distance between adjacent bright interference fringes near the center of the pattern is \(\Delta y\). Which of the following expressions correctly represents the ratio of the slit separation to the slit width, \(\dfrac{d}{a}\)?