Answer
Choice$\quad a)$
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, reworded:$\quad 57\%$ of ($23)$ is $x?$
Translated:$\quad 0.57\cdot 23=x$
Choice$\quad a)$