880 students from Experimental Primary School and some teachers took 18 identical buses to go on a spring outing. Each car has 50 seats, and each seat is full of one person. How many teachers are there for the spring outing?
实验小学880名学生和一些老师一起乘18辆同样的客车去春游．每辆车有50个座位，每个座位坐1人，正好全部坐满，参加春游的老师有多少位？
<gadget id="calculator">50 * 18</gadget>
<output>900</output>

<gadget id="calculator">900 - 880</gadget>
<output>20</output>

<result>20</result>