Add the minuend, subtrahend and difference in a subtraction formula, and the result is 120. It is known that the subtrahend is twice the difference. What is the subtrahend?
把一个减法算式里的被减数、减数与差相加，得数是120，已知减数是差的2倍，减数是多少？
<gadget id="calculator">1 + 2 + 2 + 1</gadget>
<output>6</output>

<gadget id="calculator">120 / 6</gadget>
<output>20</output>

<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<result>40</result>