There is an addition formula, Xiaohong mistook it for subtraction, and the result is 8.6, which is 10.4 less than the correct result. What is the smaller number in the original formula?
有一道加法算式，小红误当成减法，结果得8.6，比正确结果少10.4，原式中较小的数是多少．
<gadget id="calculator">8.6 + 10.4 + 8.6</gadget>
<output>27.6</output>

<gadget id="calculator">27.6 / 2</gadget>
<output>13.8</output>

<gadget id="calculator">13.8 - 8.6</gadget>
<output>5.2</output>

<result>5.2</result>