one may note, you didn't really include any "of the folllowing" ones
anyway... if we take the 3000 as the 100%, what's the 40% of that?
well [tex]\bf \begin{array}{ccllll}
amount&\%\\
\textendash\textendash\textendash\textendash\textendash\textendash&\textendash\textendash\textendash\textendash\textendash\textendash\\
3000&100\\
x&40
\end{array}\implies \cfrac{3000}{x}=\cfrac{100}{40}[/tex]
solve for "x"