Applied Sciences homework help

A 30-stack quarter-wavelength Bragg reflector is used in making a 660-nm bright-red light emitting diode (LED) on a GaAs substrate. For the stack layers, GaAs (refractive index 3.5) and Al4Ga0.6As (refractive index 3.2) are used.
a. What are the thicknesses of the GaAs and Al4Ga0.6As layers in each stack?
b. Calculate the reflectivity of the stack for 660-nm LED emission.
c. What is the bandwidth of the reflected beams in nm?