It is known that the sum of the numbers A and B is 20.58, the number of A is 7.86, what is the number of B?
已知甲、乙两数的和是20.58，甲数是7.86，乙数是多少？
<gadget id="calculator">20.58 - 7.86</gadget>
<output>12.72</output>

<result>12.72</result>