A store buys 100 pens at 5 yuan each, and sells them at 6 yuan each. Then at least how many pens are sold will earn 40 yuan in addition to recovering the cost.
某商店购进100支钢笔，每支5元，卖出时每支6元，那么至少卖出多少支，除收回成本外，还赚得40元．
<gadget id="calculator">5 * 100</gadget>
<output>500</output>

<gadget id="calculator">500 + 40</gadget>
<output>540</output>

<gadget id="calculator">540 / 6</gadget>
<output>90</output>

<result>90</result>