Just take the eigth root of the 40.
$${\sqrt[{{\mathtt{{\mathtt{8}}}}}]{{\mathtt{40}}}} = {\mathtt{1.585\: \!833\: \!175\: \!137\: \!243\: \!4}}$$
X=1.585
Just take the eigth root of the 40.
$${\sqrt[{{\mathtt{{\mathtt{8}}}}}]{{\mathtt{40}}}} = {\mathtt{1.585\: \!833\: \!175\: \!137\: \!243\: \!4}}$$
X=1.585