The school bought a pack of office paper for the sixth-grade teachers, planning to use 42 sheets per day on average, which can be used for 25 days. Due to the savings of the teachers, it actually took 35 days. How many sheets of paper are saved on average every day?
学校为六年级的老师购买了一包办公用纸，计划平均每天用42张，可以用25天．由于老师们节约，实际用了35天，平均每天节约用纸多少张？
<gadget id="calculator">25 / 35</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">42 * (5/7)</gadget>
<output>30</output>

<gadget id="calculator">42 - 30</gadget>
<output>12</output>

<result>12</result>