Monochromatic light of an unknown wavelength passes through a single slit of width 5.59 μm and forms an interference pattern on a screen 1.26 m away.  The width of the central bright fringe of the interference pattern is 18.8 cm.  The same light is then shone on potassium, a metal with a work function of 2.28 eV.

 
a)  What is the wavelength of the light in nanometers?

b)  What is the maximum speed of the electrons emitted by the metal?

Warning:  Retain many sig digs in intermediate results.  Use the accepted values of all physical constants and conversion factors accurate to three sig digs, e.g. h = 6.63e-34 Js.