A Two-Slit Apparatus Is Covered with a Red (660 Nm)

Multiple Choice

A two-slit apparatus is covered with a red (660 nm) filter.When white light is shone on the filter,on the screen beyond the two-slit apparatus,there are 9 interference minima within the 4.5 cm-wide central diffraction maximum.When a blue (440 nm) filter replaces the red,how many fringes will there be in the central diffraction maximum?

A) 3
B) 13
C) 9
D) 6