Two tuning forks A and B produce 6 beats per second when sounded together. Fork A is known to vibrate at 300Hz. When some wax is added to fork B, it is found to produce 10 beats per second with fork A, and the beat frequency is observed to increase.
(i) Find the original frequency of fork B.
(ii) Explain your reasoning clearly, showing how you decide which of the two possible values obtained must be rejected.