In a double-slit experiment, two beams of coherent light traveling different paths arrive on a screen some distance away. what is the path difference between the two waves corresponding to the third bright band out from the central bright band?

In this case, the path difference in between two waves is two wavelengths. In this double-slit experiment, the two beams of coherent light travels in different paths making the third bright band a destruction. So the difference is 2 wavelengths in between 2 waves.