$F= \frac{9}{5} \theta +32 \,\,,\,\, \theta=F$
$\theta =\frac{9}{5}\theta +32\,\Rightarrow \theta =\frac{9}{5}\theta =32\,\Rightarrow \frac{5\theta -9\theta }{5}=32\,\Rightarrow -4\theta ={{160}^{{}^\circ }}\,\Rightarrow \theta =-{{40}^{{}^\circ }}C$
$T= \theta +273 =-40+273=233K$