One number is 2.9 and the other is double it, what is the sum of these two numbers?
一个数是2.9，另一个数是它的2倍，这两个数的和是多少？
<gadget id="calculator">2.9 * 2</gadget>
<output>5.8</output>

<gadget id="calculator">2.9 + 5.8</gadget>
<output>8.7</output>

<result>8.7</result>