Aunt Wang took 40 yuan to go shopping in the market. First use 21.8 yuan to buy duck eggs, and then use the remaining money to buy apples at 5.2 yuan per kilogram. How many kilograms of apples did Aunt Wang buy? ．
王阿姨拿了40元到市场购物．买鸭蛋先用去21.8元，又用剩下的钱买每千克5.2元的苹果．王阿姨买了几千克苹果？．
<gadget id="calculator">40 - 21.8</gadget>
<output>18.2</output>

<gadget id="calculator">18.2 / 5.2</gadget>
<output>3.5</output>

<result>3.5</result>