□, △, ○ each represent a number, and satisfy the following three equations: □+□+△+○=17; □+△+△+○=14; □+△+○+○=13 ; Then what is the number represented by □.
图中的□、△、○各代表一个数字，且满足以下三个等式：□+□+△+○=17；□+△+△+○=14；□+△+○+○=13；则□代表的数字是多少．
<gadget id="calculator">17 - 11</gadget>
<output>6</output>

<result>6</result>