x = percentage (eg: if x = 3 then this represents 3%)
x/100 = decimal form of the percentage (eg: if x = 3 then x/100 = 3/100 = 0.03)
The equation to solve is
x/100 = 20/104
Cross multiply to get
104x = 100*20
104x = 2000
Then divide both sides by 104 to isolate x
104x/104 = 2000/104
x = 2000/104
x = 19.230769
x = 19.23
So the answer is approximately 19.23%