Wave interference

1) Is a property of light
2) is a property of all waves.

I think the answer is number 1. Is this correct?

I have an equation that is 6.63/8.3=0.79. I have to use the correct number of significant digits and units for my answer. Would it be 7.9 or .079?

Wave interference is a property of all waves, including sound waves. When the crests of two waves coincide, it is constructive interference; when the crest of a wave coincides with the trough of another wave it is destructive interference.

The answer would be 0.80. The second zero shows you answer is limited to two significant digits. Your calculator shows 0.7988, so round up to 0.80