There are red and white glass balls in the box. The number of red balls is 2 times more than that of white balls. Take 7 white balls and 15 red balls from the box each time. There are 8 red balls left, how many more red balls are there than white balls in the box?
箱子里有红、白两种颜色的玻璃球，红球的个数比白球的3倍多2个，每次从箱子里取7个白球，15个红球，经过若干次后，箱子里只剩下8个红球，箱子里原来的红球数比白球数多多少个？
<gadget id="calculator">8 / 15</gadget>
<output>8/15 = around 0.533333</output>

<gadget id="calculator">2 / 15</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">(8/15) - (2/15)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">3 / 15</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">(1/5) - (1/7)</gadget>
<output>2/35 = around 0.057143</output>

<gadget id="calculator">(2/5) / (2/35)</gadget>
<output>7</output>

<gadget id="calculator">3 * 7</gadget>
<output>21</output>

<gadget id="calculator">2 - 7</gadget>
<output>-5</output>

<gadget id="calculator">21 + (-5)</gadget>
<output>16</output>

<result>16</result>