How do you determine the frequency of a wave of a string with one end attached to a weight in water?

In a laboratory experiment, one end of a horizontal string is tied to a support while the other end pes over a frictionless pulley and is tied to a 3.0 kg sphere. Students determine the frequencies of standing waves on the horizontal segment of the string, then they raise a beaker of water until the hanging 3.0 kg sphere is completely submerged. The frequency of the fifth harmonic with the sphere submerged exactly matches the frequency of the third harmonic before the sphere was submerged. What is the diameter of the sphere?