Please use 5 3s and appropriate operation symbols and parentheses to form a calculation formula so that the result is equal to 11. What is this formula.
请你用5个3和恰当的运算符号及括号组成一道算式，使其结果等于11．这个算式是多少．
<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">3 / 3</gadget>
<output>1</output>

<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">9 + 2</gadget>
<output>11</output>

<result>11</result>