Double slit experiment with smoke particles

1. The problem statement, all variables and given/known data
Suppose we wish to do a double slit experiment with a beam of the smoke particles of Example 4.1c (which is lamda=6.6e-20m). Assume we can construct a double slit whose seperation is about the same size of the particles. Estimate the seperation between the fringes if the double slit and the screen were on opposite coasts of the United States.


2. Relevant equations
2dsin(theta)=n(lamda)
lamda=h/p


3. The attempt at a solution
Well I see how they got lamda and I understand that I am looking for the seperation between the fringes. And that the seperation between the slits is 6.6e-20 meters. Honestly I would show work if I understood what was happening here but im confused. I am confused on how to find theta or un less I assume n=1 but I still dont know lamda.

 

Yah sorry and you are correct it is de broglies wavelength but how should I start this?

 

D is slit width is the angl found from the incident beam, the 2 comes from the distance from the second level of atoms and n stands for the number of maximums and finally lambda stands for the wavelength