First add 4 to a number, then divide by 4, then subtract 6, and then multiply by 5, the result is 75, what is this number?
一个数先加4，再除以4，然后减去6，再乘以5，结果是75，这个数是多少．
<gadget id="calculator">75 / 5</gadget>
<output>15</output>

<gadget id="calculator">15 + 6</gadget>
<output>21</output>

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

<gadget id="calculator">84 - 4</gadget>
<output>80</output>

<result>80</result>