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# System prepended metadata

title: HackMD

---

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