Teacher Wang bought a pack of white paper and planned to use 20 sheets per day, which can be used for 28 days. Because he paid attention to saving paper, he actually used 4 sheets less than planned every day. How many days more than planned?
王老师买来一包白纸，计划每天用20张，可以用28天，由于注意了节约用纸，实际每天比计划少用4张，实际比计划多用多少天？
<gadget id="calculator">560 / 14</gadget>
<output>40</output>

<gadget id="calculator">40 - 28</gadget>
<output>12</output>

<result>12</result>