You have
[tex]\dfrac{x}{20}=\dfrac{4}{5}[/tex]
Multiply both sides by 20:
[tex]20\cdot\dfrac{x}{20}=\dfrac{4}{5}\cdot 20[/tex]
The equation becomes
[tex]x=16[/tex]
Hi
X/20 = 4/5 ⇒ X = 20*4 /5 = 5*4*4 /5 = 16/1 =16
16/20 = 4/5
