=> \(K = \frac{1}{{35}}\) Again \(\frac{{344 - 342}}{t} = \frac{1}{{35}}\left[ {\frac{{344 - 342}}{2} - 293} \right] = \frac{{10}}{7}\)
==> \(t = \frac{{14}}{{10}}\)min = \(\frac{{14}}{{10}} \times 60 = 84\)sec.
[Assume steady state heat conduction]