For a string stretched between two supports, two successive standing-wave frequencies are 510 Hz and 680 Hz. There are also other standing waves with...

 For a string stretched between two supports, two successive standing-wave frequencies are 510 Hz and 680 Hz. There are also other standing waves with higher and lower frequencies. What is the order of these two harmonics (first, second, etc.)? If the speed of the propagation of transverse waves is 85 m/s what is the length of the string