As per the question,
$\frac{\left({ }^{14} \mathrm{C} / 12 \mathrm{C}\right)_{\text {wood }}}{\left({ }^{14} \mathrm{C} /{ }^{12} \mathrm{C}\right)_{\text {atrmophere }}}=\frac{1}{8}$
So, $\lambda \mathrm{t}=\ln 8$
$\frac{\ln 2}{t_{1 / 2}} t=\ln 8$
$t=3 \times t_{1 / 2}=17190 \text { years }$
(નજીકનાં પૂર્ણાકમાં રાઉન્ડ ઑફ) $\left[ R =8.314\, J \,K ^{-1} \,mol ^{-1}\right]$