let's say is "x", so "x" is the 100%, and we know that 37 is the 31%, so, what's "x"?
[tex]\bf \begin{array}{ccll}
amount&\%\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
37&31\\
x&100
\end{array}\implies \cfrac{37}{x}=\cfrac{31}{100}\implies \cfrac{37\cdot 100}{31}=x[/tex]
