In a subtraction formula, the sum of the minuend, the subtrahend, and the difference is 120, and the difference is three times the subtrahend. What is the difference?
有一道减法算式中，被减数、减数、差的和是120，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">120 / 8</gadget>
<output>15</output>

<gadget id="calculator">3 * 15</gadget>
<output>45</output>

<result>45</result>