If one addend is decreased by 0.5, how much should the other addend be increased if the sum is to be increased by 8.9
一个加数减少0.5，如果要使和增加8.9，另一个加数应增加多少
<gadget id="calculator">8.9 + 0.5</gadget>
<output>9.4</output>

<result>9.4</result>