Write 12 as the sum of two numbers a and b, to maximize the product of a and b, then ab=how much.
把12写成两个数a与b的和，要使a与b的乘积最大，那么a-b=多少．
<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">6 - 6</gadget>
<output>0</output>

<result>0</result>