Question

What happens if two sound waves having the same frequency interfere in phase?

Answer 1

two things are to be noted. One that they have the same frequency, second that they're in phase. Since they have the same frequency, they will cover the same distance over time. And since they're in phase, the crest will match the crest and the trough will match with trough.

because of this matching there will be an amplification

superimposition Will occur. And The amplitude of the two waves that we added