The fruit wholesale station shipped three kinds of fruits, of which 20 boxes were not apples, and 18 boxes were not pears. It is known that there are 22 boxes of apples and pears. How many boxes of oranges are there?
水果批发站运到三种水果，其中有20箱不是苹果，有18箱不是梨，已知苹果和梨共有22箱，桔子有多少箱．
<gadget id="calculator">18 - 22</gadget>
<output>-4</output>

<gadget id="calculator">20 + (-4)</gadget>
<output>16</output>

<gadget id="calculator">16 / 2</gadget>
<output>8</output>

<result>8</result>