In a forest farm, a total of 840 willows and poplars are newly planted, and 570 poplars are known to be planted. How many willows are planted?
某林场，新种植柳树和杨树共840棵，已知种杨树570棵，种柳树多少棵？
<gadget id="calculator">840 - 570</gadget>
<output>270</output>

<result>270</result>