T = \sqrt[4]{\frac{E_{T}}{σ}} = \sqrt[4]{\frac{240}{5, 67 \times 10^{- 8}}} = 255 K = - 18^{\circ} C

${T=\sqrt[4]{\frac{E_T}{\sigma}}=\sqrt[4]{\frac{240}{5,67 \times 10^{-8}}}= \mathrm{ 255\, K=-18 ^\circ C}}$

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