Li Ming was doing an arithmetic problem. It was supposed to divide a certain number by 7, and then add 72. Due to his carelessness, the division was made into multiplication, and the addition was made into subtraction. But the answer is still correct. Do you know what a certain number is?
李明同学做一道算术题，本来应是某数除以7，然后加72，由于他粗心，除法做成乘法，加法做成减法，可是答案还是对的，你知道某数是什么数吗？
<gadget id="calculator">72 - 0</gadget>
<output>72</output>

<gadget id="calculator">72 + 72</gadget>
<output>144</output>

<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">7 - (1/7)</gadget>
<output>48/7 = around 6.857143</output>

<gadget id="calculator">144 / (48/7)</gadget>
<output>21</output>

<result>21</result>