A standing wave is established in a 120-cm-long string f xed at both ends. the string vibrates in four segments when driven at 120 hz. (a) determine the wavelength

IF the question says there are 4 segments, remember this rule:

number of wavelengths on a string = the number of segments divided by 2.

Once you know the number of wavelengths simply divide the length of the string by the wavelength:

string length / number of wavelengths = wavelength

120cm / 2 wavelengths = 10cm per wavelength

so the wavelength = 10cm