Subtract 9 from a number, multiply by 4, and add 9 to get 57. What is this number?
某数减去9，乘以4，再加9，得到57．这个数是多少？
<gadget id="calculator">9 * 4</gadget>
<output>36</output>

<gadget id="calculator">57 - 9</gadget>
<output>48</output>

<gadget id="calculator">36 + 48</gadget>
<output>84</output>

<gadget id="calculator">84 / 4</gadget>
<output>21</output>

<result>21</result>