Add the minuend, subtrahend and difference of a subtraction expression, and the result is 990. It is known that the subtrahend is twice the difference. What is the subtraction.
把一个减法算式的被减数、减数与差相加，得数是990．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">990 / 6</gadget>
<output>165</output>

<gadget id="calculator">165 * 2</gadget>
<output>330</output>

<result>330</result>