In a subtraction formula, the sum of the minuend, the subtrahend, and the difference is 8, and the subtrahend is 1.8. What is the difference?
在一道减法算式里，被减数、减数、差的和是8，减数是1.8，差是多少
<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">4 - 1.8</gadget>
<output>2.2</output>

<result>2.2</result>