The sum of the numbers A and B is 48.7, and the number B is 27.98. What is the number A?
甲、乙两数的和是48.7，乙数是27.98，甲数是多少？
<gadget id="calculator">48.7 - 27.98</gadget>
<output>20.72</output>

<result>20.72</result>