AMC 12 2005b Problem 2

A positive number $x$ has the property that $x\%$ of $x$ is $4$. What is $x$?

$\mathrm{(A)}\ 2 \mathrm{(B)}\ 4 \mathrm{(C)}\ 10 \mathrm{(D)}\ 20 \mathrm{(E)}\ 40$