My mother bought a bottle of salad oil, which weighed 3.4 kg in total, and after half of it was used up, the total weight of the bottle was 1.9 kg. What is the original net weight of this bottle of oil?
妈妈买了一瓶色拉油，连瓶共重3.4千克，用去一半后连瓶共重1.9千克．问这瓶油原来净重多少千克？
<gadget id="calculator">3.4 - 1.9</gadget>
<output>1.5</output>

<gadget id="calculator">1.5 * 2</gadget>
<output>3</output>

<result>3</result>