In a subtraction formula, the sum of the minuend, the subtrahend, and the difference is 80, and the difference is exactly 3 times the subtrahend, what is the difference
在一个减法算式里，被减数，减数，差的和是80，而且差正好是减数的3倍，差是多少
<gadget id="calculator">40 / 4</gadget>
<output>10</output>

<gadget id="calculator">10 * 3</gadget>
<output>30</output>

<result>30</result>