A stationery store buys a batch of pens, the purchase price is 11 yuan each, and the selling price is 14 yuan each. There are still 50 pens in the store now, and the full cost has been recovered at this time, and the profit is 140 yuan. How many pens are there in this batch?
文具店购进一批钢笔，进价是每支11元，售价是每支14元．现在商店还有50支笔，这时已经收回了全部成本，并且盈利140元．求这批钢笔共有多少支？
<gadget id="calculator">50 * 14</gadget>
<output>700</output>

<gadget id="calculator">700 + 140</gadget>
<output>840</output>

<gadget id="calculator">14 - 11</gadget>
<output>3</output>

<gadget id="calculator">840 / 3</gadget>
<output>280</output>

<result>280</result>