There are 25 red, blue and white gemstones in a necklace. If there are 8 more rubies than sapphires and 4 more sapphires than white gemstones, how many rubies are there?
一串项链上有红、蓝、白三色的宝石共25颗，如果其中红宝石比蓝宝石多8颗，蓝宝石比白宝石多4颗，那么红宝石有多少颗．
<gadget id="calculator">8 + 4</gadget>
<output>12</output>

<gadget id="calculator">25 - 12 - 4</gadget>
<output>9</output>

<gadget id="calculator">9 / 3</gadget>
<output>3</output>

<gadget id="calculator">3 + 4 + 8</gadget>
<output>15</output>

<result>15</result>