so, we know he submitted 3 already, and his teacher said that is 20%, let's say "x" is the 100%.
[tex]\bf \begin{array}{ccll}
amount&\%\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
3&20\\
x&100
\end{array}\implies \cfrac{3}{x}=\cfrac{20}{100}\implies \cfrac{3\cdot 100}{20}=x[/tex]
