PLEASE HELP! I WILL MARK BRAINLIEST! tight guitar string has a frequency of 560 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of its original length?

Amichelson interferometer operating at a 600 nm wavelength has a 3.02-cm-long glass cell in one arm. to begin, the air is pumped out of the cell and mirror m2 is adjusted to produce a bright spot at the center of the interference pattern. then a valve is opened and air is slowly admitted into the cell. the index of refraction of air at 1.00 atm pressure is 1.00028.how many bright-dark-bright fringe shifts are observed as the cell fills with air?