Finding 2nd Dark Fringe Angle for Diffraction Single Slit 1.5x10^6m

[Laceb04]

A single slit has a width of 1.5 x 10^6 m and is used to form a diffraction pattern. Find the angle that locates the second dark fringe when the wavelength of the light is each of the following.

(a) 425 nm

(b) 650 nm


I answered with (a) 16.46 and (b) 25.68 but these answers are wrong

 

[Päällikkö]

You're asked for the second dark fringes, which I suppose means n = 2 in the equation
$$d \sin\theta = n\lambda$$
(you've apparently used n = 1)