Two slits are 0.158 mm apart. A mixture of red light ( wavelength = 65 nm) and yellow green light (wavelength = 565 nm)falls on the slits. A flat observation screen is located 2.24 m away. What's the distance on the screen between the third order red fringe and the third order yellow green fringe?

Answer 1

take each wavelength: calcute the distance from center for each wavelength at that order.
then subtract. http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/slits.html