Standing waves and frequency

[bigsaucy]

1.) A string, stretched between two fixed posts, forms standing-wave resonances at 325Hz and 390Hz. What is the largest possible value of its fundamental frequency?

I have no idea on how to solve this problem, any assistance would be greatly appreciated.

 

[HallsofIvy]

Any frequency must be an integer multiple of the fundamental frequency. What is the largest integer that divides both 325 and 390?

 

[bigsaucy]

would it be 65Hz?