I need proficient help in the following problem:
Problem: You are working with an electrical engineer who wants to send you messages with his microwave antenna. The engineer points his antenna at a narrow window (width 36.0 cm) of your building and starts sending microwaves (wavelength 5.40 cm) your way.
A - What is the location of the first "dark" fringe on the wall 6.65 m from the window?
=_____ cm
If possible just a brief explanation how you got the answer?