A two-slit apparatus is covered with a red (643 nm) filter. When white light is shone on the filter, on the screen beyond the two-slit apparatus, there are nine interference maxima within the 4.11-cm-wide central diffraction maximum.
a) When a blue (423 nm) filter replaces the red, how many interference maxima will there be in the central diffraction maximum?
b) And how wide will that diffraction maximum be?