Four times a number minus the number itself, the difference is 25.2, find this number. (solution by equation)
一个数的4倍减去这个数的本身，差是25.2，求这个数．(用方程解)
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">25.2 / 3</gadget>
<output>8.4</output>

<result>8.4</result>