It is known that the sum of the numbers A and B is 31.56, the number B is 12.68, what is the number A?
已知A、B两数的和是31.56，B数是12.68，A数是多少？
<gadget id="calculator">31.56 - 12.68</gadget>
<output>18.88</output>

<result>18.88</result>