To make 18/(○+3)=2 established, how much should be filled in ○.
要使18/(○+3)=2成立，○里应该填多少．
<gadget id="calculator">18 / 2</gadget>
<output>9</output>

<gadget id="calculator">9 - 3</gadget>
<output>6</output>

<result>6</result>