Question

42 is 21% of what number

Answer 1

$\begin{array}{ccc}42&-&21\%\\x&-&100\%\end{array}\ \ \ \ \ |cross\ multiply\\\\21x=42\times100\\\\21x=4200\ \ \ \ \ |divide\ both\ sides\ by\ 21\\\\\boxed{x=200}\leftarrow answer$

Answer 2

42/x =21/100
21x=4200
x=200
The answer is 200