5: How much should be added to the former item of 12 plus the latter item of 15.
5：12的前项加上15后项应该加上多少．
<gadget id="calculator">5 + 15</gadget>
<output>20</output>

<gadget id="calculator">20 / 5</gadget>
<output>4</output>

<gadget id="calculator">12 * 4</gadget>
<output>48</output>

<gadget id="calculator">48 - 12</gadget>
<output>36</output>

<result>36</result>