Solve the following problem:

Problem: One day, after pulling down your window shade, you notice that sunlight is passing through a pinhole in the shade and making a small patch of light on the far wall. Having recently studied optics in your physics class, you're not too surprised to see that the patch of light seems to be a circular diffraction pattern. It appears that the central maximum is about 3 cm across, and you estimate the distance from the window shade to the wall is about 2 m. Know that the average wavelength of sunlight is about 500 nm,

Part A: Estimate the diameter of the pinhole?

______mm

Please show all work and steps to determine the diameter of the pinhole.