\(x = 6\, bps,\) which is decreasing (i.e. \(x\downarrow\))
after loading (from \(6\) to \(1\, bps\))
Unknown tuning fork is loaded so \(n_B\downarrow\)
Hence \(n_A -n_B\downarrow = x\downarrow\) ... \((i)\) \(\rightarrow\) Wrong
\(n_B\downarrow -n_A = x\downarrow\) ... \((ii)\) \(\rightarrow\) Correct
\(\Rightarrow\)\(n_B = n_A + x = 341 + 6 = 347 Hz.\)