It costs 70 yuan to buy a table, b yuan to buy a chair, how much does it cost to buy 4 sets of tables and chairs.
买一张桌子要70元，买一把椅子要b元，买4套桌椅需多少元．
<gadget id="calculator">70 * 4</gadget>
<output>280</output>

<gadget id="calculator">280 + 4</gadget>
<output>284</output>

<result>284</result>