□/☆=7…9, the minimum number in □ can be filled.
□/☆=7…9，□里的数最小可以填多少．
<gadget id="calculator">9 + 1</gadget>
<output>10</output>

<gadget id="calculator">7 * 10</gadget>
<output>70</output>

<gadget id="calculator">70 + 9</gadget>
<output>79</output>

<result>79</result>