There used to be some trees in the school, but 80 were planted this year, and now there are 250 trees in total. How many trees did the school have?
学校原来有一些树，今年又栽了80棵，现在一共有树250棵．学校原来有树多少棵？
<gadget id="calculator">250 - 80</gadget>
<output>170</output>

<result>170</result>