The number A is 8.6, and the number B is 6.9. Use the sum of the two numbers and subtract their difference to get the number.
甲数是8.6，乙数是6.9，用两数之和，减去它们的差，得多少．
<gadget id="calculator">8.6 + 6.9</gadget>
<output>15.5</output>

<gadget id="calculator">8.6 - 6.9</gadget>
<output>1.7</output>

<gadget id="calculator">15.5 - 1.7</gadget>
<output>13.8</output>

<result>13.8</result>