Use 6 yuan per kilogram of grade A sugar, 3.5 yuan per kilogram of B grade sugar, and 3 yuan per kilogram of C grade sugar, and mix them into 4 yuan per kilogram of assorted sugar. , How many kilograms of B sugar should be added.
用6元1千克的甲级糖，3.5元1千克的乙级糖，3元1千克的丙级糖，混合成每千克4元的什锦糖，如果甲级糖1千克，丙级糖1千克，应加乙级糖多少千克．
<gadget id="calculator">3 - 4 - 4</gadget>
<output>-5</output>

<gadget id="calculator">6 + (-5)</gadget>
<output>1</output>

<gadget id="calculator">4 - 3.5</gadget>
<output>0.5</output>

<gadget id="calculator">1 / 0.5</gadget>
<output>2</output>

<result>2</result>