Wang Qiang did an arithmetic problem. The original problem was to divide "a certain number" by 7 and then add 72. Because of his carelessness, the division was made into multiplication, and the addition was made into subtraction, but the answer was still correct. So what is the number?
王强做算术题，原题是"某数"除以7然后加72，由于他为粗心，除法做成乘法，加法做成减法，可是答还是对的．那么该数是多少？
<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>