A beam of electrons is accelerated across a potential of 13.30 kV before passing through two slits. The electrons form an interference pattern on a screen 5.00 m in front of the slits. The first-order maximum is 8.20 mm from the central maximum. What is the distance between the slits?

I know the answer is 6.48 nm, however after multiple attempts I am still far away I had 7.12. please help me figure out how to get to 6.48nm