A bottle of oil weighs 3.7 kilograms. After half of the oil is poured out, the weight of the bottle is 2.1 kilograms. How much is the original oil in the bottle?
一瓶油连瓶重3.7千克，倒出油的一半后，连瓶重2.1千克，瓶里原有油多少千克．
<gadget id="calculator">3.7 - 2.1</gadget>
<output>1.6</output>

<gadget id="calculator">1.6 * 2</gadget>
<output>3.2</output>

<result>3.2</result>