It is defined that a string that is in its two ends, its fundamental frequency and its subsequent frequencies are the product of the whole depending on the number of the harmonic. In other words, harmonics (higher) define the subsequent frequencies under the functions 2f, 3f, 4f, 5f, etc.
Therefore we have that the higher harmonics would be:
1 x 80 Hz = 80 Hz (1st harmonic and Fundalmental Frequency)
2 x 80Hz = 160Hz (2nd harmonic)
3 x 80Hz = 240Hz (3rd harmonic)
4 x 80Hz = 320Hz (4th harmonic)
5 x 80Hz = 400Hz (5th harmonic)
Hence, the frequencies 160Hz and 240Hz are the two higher harmonics of string with a fundamental frequency of 80Hz.
