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# System prepended metadata

title: Untitled

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#HackMD
##hackmd
\begin{align}
s(x)=\begin{cases}
-4x+31&\text{ if } 0\le x \le 12\\
295&\text{ if }12<x\le20\\
\frac{4}{3}x+278.5 &\text{ if } 20<x\le30\\
\frac{3}{2}x+404 &\text{ if } 30<x<40\\
     \end{cases}
\end{align}

