Step-by-step explanation:
It is given that,
Frequency of violin string tuned to, 

Beat frequency, 

Number of beats per second is given by :



Either 
 or 
 
When the guitar string is tightened, and the beat frequency is found to increase, then the original frequency will decrease.
So, the original frequency of the guitar string is 482.4 Hz. Hence, this is the required solution.