<td style="text-align:right;">21</td>
      <td style="text-align:center;">&#128522;</td>
      <td style="text-align:left;">$$\begin{matrix}
 f & = & 2 + x + 3 \\
 & = & 5 + x 
\end{matrix}$$</td>
      <td style="text-align:left;"><section><eqn><span class="katex-display"><span class="katex"><span class="katex-mathml"><math><semantics><mrow><mtable><mtr><mtd><mrow><mi>f</mi></mrow></mtd><mtd><mrow><mo>=</mo></mrow></mtd><mtd><mrow><mn>2</mn><mo>+</mo><mi>x</mi><mo>+</mo><mn>3</mn></mrow></mtd></mtr><mtr><