There is a meadow, 17 horses can eat the grass in 30 days, and 19 horses can eat the grass in 24 days. After 6 days of eating some horses, sell 4 horses, and the remaining horses can eat the grass in 2 days No, how many horses were grazing before selling?
有一草地，17匹马30天可把草吃没，19匹马24天可以吃没，现有若干匹马吃了6天后，卖了4匹马，剩下的马再吃2天把草吃没，则卖之前有几匹马在吃草？
<gadget id="calculator">17 * 30</gadget>
<output>510</output>

<gadget id="calculator">19 * 24</gadget>
<output>456</output>

<gadget id="calculator">510 - 456</gadget>
<output>54</output>

<gadget id="calculator">30 - 24</gadget>
<output>6</output>

<gadget id="calculator">54 / 6</gadget>
<output>9</output>

<gadget id="calculator">17 - 9</gadget>
<output>8</output>

<gadget id="calculator">8 * 30</gadget>
<output>240</output>

<gadget id="calculator">8 * 9</gadget>
<output>72</output>

<gadget id="calculator">240 + 72</gadget>
<output>312</output>

<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<gadget id="calculator">312 + 8</gadget>
<output>320</output>

<gadget id="calculator">320 / 8</gadget>
<output>40</output>

<result>40</result>