A) To calculate the angle at which the first minimum occurs for 405nm light, we need to use the equation θ = λ/d, where θ is the angle in degrees, λ is the wavelength of the light, and d is the slit width. Thus, for 405nm light, we have θ = 405nm/2.5um = 162°.
B) To calculate the angle for 740nm light, we can use the same equation, so θ = 740nm/2.5um = 296°. Thus, the first minimum for 740nm light occurs at an angle of 296°.