In a Young's double slit experiment, the distance between the slits and the screen is 1.60m and using light of wavelength 5.89x10^-7m the distance between the centre of the interference pattern and the fourth bright fringe on either side is 16.0mm. What is the slit separation?

I know about the equation w = λD/s

where w is the fringe separation,

D is the distance from slits to screen

and s is the slit spacing.

The problem I'm having is the w value. "the distance between the centre of the interference pattern and the fourth bright fringe on either side is 16.0mm." Any ideas?

Thanks in advance.