The kindergarten bought 15 boxes of pencils, 3 boxes of crayons more than pencils, and twice as many watercolor pens as crayons. How many boxes of watercolor pens did you buy?
幼儿园买了15盒铅笔，买的蜡笔比铅笔多3盒，买的水彩笔是蜡笔的2倍．买了水彩笔多少盒？
<gadget id="calculator">15 + 3</gadget>
<output>18</output>

<gadget id="calculator">18 * 2</gadget>
<output>36</output>

<result>36</result>