$${\mathtt{50}} = {\frac{{\mathtt{131.4}}{\mathtt{\,\times\,}}{log}_{10}\left({\mathtt{3}}\right)}{{\mathtt{d}}}}$$
$${\mathtt{50}}{\mathtt{\,\times\,}}{\mathtt{d}} = {\mathtt{131.4}}{\mathtt{\,\times\,}}{\mathtt{log3}}$$ => $${\mathtt{d}} = {\frac{{\mathtt{131.4}}{\mathtt{\,\times\,}}{log}_{10}\left({\mathtt{3}}\right)}{{\mathtt{50}}}}$$
$${\mathtt{50}} = {\frac{{\mathtt{131.4}}{\mathtt{\,\times\,}}{log}_{10}\left({\mathtt{3}}\right)}{{\mathtt{d}}}}$$
$${\mathtt{50}}{\mathtt{\,\times\,}}{\mathtt{d}} = {\mathtt{131.4}}{\mathtt{\,\times\,}}{\mathtt{log3}}$$ => $${\mathtt{d}} = {\frac{{\mathtt{131.4}}{\mathtt{\,\times\,}}{log}_{10}\left({\mathtt{3}}\right)}{{\mathtt{50}}}}$$