Given, f=340Hz Let beat frequency of tuning fork A is fA and fA′ be the frequency of tuning fork A after filling. In first case, beat frequency =5 ⇒‌fA=340±5 ⇒‌fA=345Hz‌ or ‌335Hz After filling tuning fork A,fA′=340±2 ⇒‌‌fA′=342‌ or ‌338Hz As on filling, frequency of A increases. Hence, original frequency of tuning fork A is 335Hz.