The first dark ring forms the boundary for the bright airy

Question

Question: Consider light from a helium-neon laser (λ=632.8 nanometers) striking a pinhole with a diameter of 0.475 mm

PART A.At what angle θ1 to the normal would the first dark ring be observed?ANSWER is 9.31*10^-2

PART B. Suppose that the light from the pinhole projects onto a screen 3.00 meters away. What is the radius r1 of the first dark ring on that screen? Notice that the angle from Part A is small enough that sinθ≈tanθ. ANSWER is 4.88 mm

PART C. The first dark ring forms the boundary for the bright Airy disk at the center of the diffraction pattern. What is the area A of the Airy disk on the screen from Part b?

PART D. What is the angular radius θ1 of the first dark ring for a point source being imaged by this telescope? Use 550 nanometers for the wavelength, since this is near the average for visible light.