In a subtraction formula, the sum of the minuend, the subtrahend and the difference is 21.6. It is known that the subtrahend is 5 times the difference. What is the subtrahend?
在一道减法算式中，被减数、减数与差的和是21.6，已知减数是差的5倍，减数是多少．
<gadget id="calculator">1 + 5 + 5 + 1</gadget>
<output>12</output>

<gadget id="calculator">21.6 / 12</gadget>
<output>1.8</output>

<gadget id="calculator">1.8 * 5</gadget>
<output>9</output>

<result>9</result>