In a subtraction formula, the sum of the minuend, the subtrahend, and the difference is 80, and the difference is three times the subtrahend. What is the difference?
一个减法算式中，被减数、减数、差的和是80，且差是减数的3倍，差是多少．
<gadget id="calculator">1 + 3 + 1 + 3</gadget>
<output>8</output>

<gadget id="calculator">80 / 8</gadget>
<output>10</output>

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

<result>30</result>