A chair is 90 yuan, a table is 70 yuan more expensive than a chair, a sofa is 400 yuan more expensive than a table, how much is a sofa.
一把椅子90元，一张桌子比椅子贵70元，一个沙发比桌子贵400元，一个沙发多少元．
<gadget id="calculator">90 + 70 + 400</gadget>
<output>560</output>

<result>560</result>