Xiaohong, Xiaojun and Xiaoming are 21 years old this year, Xiaohong and Xiaojun are 13 years old, Xiaojun and Xiaoming are 15 years old, how old are Xiaoming and Xiaohong this year?
今年小红、小军和小明共21岁，其中小红和小军共13岁，小军和小明共15岁，小明和小红今年共多少岁？
<gadget id="calculator">15 - 21</gadget>
<output>-6</output>

<gadget id="calculator">13 + (-6)</gadget>
<output>7</output>

<gadget id="calculator">15 - 7</gadget>
<output>8</output>

<gadget id="calculator">13 - 7</gadget>
<output>6</output>

<gadget id="calculator">8 + 6</gadget>
<output>14</output>

<result>14</result>