if we take 4c to be the 100%, what is 0.2c off of it in percentage?
[tex]\begin{array}{ccll} a&b\\ \cline{1-2} 4c & 100\\ 0.2c& x \end{array} \implies \cfrac{4c}{0.2c}~~=~~\cfrac{100}{x}\implies \cfrac{4}{0.2}~~ = ~~\cfrac{100}{x} \\\\\\ 4x=20\implies x=\cfrac{20}{4}\implies x=5[/tex]