Answer
$ 22.5\%$
Work Step by Step
Typical percentage problem:
What percent ($n$, as a decimal number) of (the base amount $y)$ is $x?$
Translated:$\quad n\cdot y=x$
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Here, What percent ($n$, as a decimal number) of ($y=40$) is ($x=9$)$?$
Translated:$\quad n\cdot 40=9$
... divide with $40$
$ n=0.225\qquad$ .... convert to percent notation,
( move the decimal point two places to the right and write a percent symbol.)
$=22.5\%$