In a box containing pens of various colors, the number of black pens accounts for the total number (5/12), and later 18 black pens are put in. At this time, the ratio of the number of black pens to the number of other color pens is 2 : 1. How many black pens are there in total now?
一个装有各种颜色的钢笔的盒中，黑色钢笔枝数占总数的(5/12)，后来又放进18枝黑色钢笔，这时黑色钢笔枝数与其他颜色钢笔枝数的比是2：1，现在共有黑色钢笔多少枝？
<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">2 - (5/7)</gadget>
<output>9/7 = around 1.285714</output>

<gadget id="calculator">18 / (9/7)</gadget>
<output>14</output>

<gadget id="calculator">14 * 2</gadget>
<output>28</output>

<result>28</result>