Kindergarten teacher Li went to buy fruit, she bought 4 watermelons, the quantity of pineapples she bought was half of the watermelons, and the quantity of peaches she bought was 3 times less than the total of watermelons and pineapples. The peaches that Teacher Li bought were how many?
幼儿园李老师去买水果，她买来4个西瓜，买来菠萝的数量是西瓜的一半，买来的桃子的数量比西瓜和菠萝的总数的3倍少3个，李老师买来的桃子是多少个？
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">4 + 2</gadget>
<output>6</output>

<gadget id="calculator">6 * 3</gadget>
<output>18</output>

<gadget id="calculator">18 - 3</gadget>
<output>15</output>

<result>15</result>