A silicon wafer is coated with a wedge-shaped layer of silicon dioxide (index of refraction \(n_f\)) resting on a silicon substrate (index of refraction \(n_s\)). The indices of refraction satisfy \(1 < n_f < n_s\). The film thickness increases linearly with horizontal position \(x\) according to \(t(x) = C x\), where \(C\) is a positive constant and \(x = 0\) corresponds to the edge of the film. Monochromatic light of wavelength \(\lambda\) in air strikes the film at normal incidence. Which of the following expressions represents the distance \(x_1\) from the edge (\(x = 0\)) to the first bright fringe observed at a position \(x > 0\) in reflection?