Hi there! I am having trouble with the following question:

Plasticine (which lowers the pitch) is added to one tine of the tuning forks of unknown frequency referred to in question #4 (initial frequency = 300 Hz possible frequencies 303 Hz or 297 Hz). The number of beats decreases to one(per second). What was the frequency of the unknown fork?

Well, i know how to calculate the beat difference, but I do not under stand which of the 303Hz or the 297Hz referred to question #4 are the correct initial frequencies before adding the Plasticine!!! Can some one explain that to me please!

Thank you for your time.