Cross Multiplying and Simplifying

Question

In a YouTube video by Michael Penn, at the 3:56 mark, he gets the equation: $$ \frac{4}{2} = \frac{2}{2-x}\Rightarrow 8-4x=4$$ Could someone explain to me how he does this and the process behind it? Thanks for your help! (Im only freshman year of high school so sorry if this question seems basic)

Answer 1

The domain is $x\neq2$ and we obtain: $$\frac{4}{2}\cdot2(2-x)=\frac{2}{2-x}\cdot2(2-x),$$ which gives $$4(2-x)=4$$ or $$8-4x=4.$$ Here $2(2-x)$ it's a common denominator of the left side and the right side of the equation.