In a subtraction formula, the sum of the minuend, the subtrahend and the difference is equal to 120, and the difference is 3 times the subtrahend, then what is the difference.
在一个减法算式里，被减数、减数与差的和等于120，而差是减数的3倍，那么差等于多少．
<gadget id="calculator">120 / 2</gadget>
<output>60</output>

<gadget id="calculator">1 + 3</gadget>
<output>4</output>

<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">60 * (3/4)</gadget>
<output>45</output>

<result>45</result>