```html
<p>2 + 4 = <span onclick='this.document.getElementsByTagName("p").item(0).innerHTML = eval(2+4)'>답</span></p>
<p>4 * 20 + 64 = <span onclick='this.document.getElementsByTagName("p").item(1).innerHTML = eval(4*20+64)'>답</span></p>
<p>20 / 5 - 8 * 2 = <span onclick='this.document.getElementsByTagName("p").item(2).innerHTML = 20/5 - 8*2'>답</span></p>
```

I want to click “답” to output answers to mathematical expressionsbut， doesn't work