Calculate $X$ of a math problem

Question

I am trying to learn some more math and I got stuck on this:

$$\frac{0.2}{X} = 140$$

How do I calculate $X$?

EDIT

Sorry I meant to calculate $$\frac{28}{X} = 140$$

So that $X = 0.2$, but how do I calculate it?

Answer 1

$$\begin{align}\frac{0.2}{X}=140&\Rightarrow \frac{0.2}{X}\times X=140\times X\\&\Rightarrow 0.2=140X\\&\Rightarrow 0.2\times\frac{1}{140}=140X\times\frac{1}{140}\\&\Rightarrow \frac{0.2}{140}=X\\&\Rightarrow X=\frac{0.2\times 10}{140\times 10}=\frac{2}{1400}=\frac{1}{700}.\end{align}$$

P.S. 1 : Multiplying the both sides of $$\frac{0.2}{X}=140$$by X gives us $$\frac{0.2}{X}\times X=140\times X$$ i.e. $$0.2=140X.$$

P.S. 2 : Multiplying the both sides of $$\frac{28}{X}=140$$ by $X$ gives us $$\frac{28}{X}\times X=140\times X$$ i.e. $$28=140X.$$ Then, multiplying the both sides by $\frac{1}{140}$ gives us $$28\times\frac{1}{140}=140X\times\frac{1}{140}$$ i.e. $$\frac{28}{140}=X.$$

Then, we have $$X=\frac{28}{140}=\frac{28}{28\times 5}=\frac{1}{5}=0.2.$$