A bottle of oil, 1.6 kg is used for the first time, and the rest (3/4) is used for the second time, and there is still 2.1 kg of oil in the bottle. How much does this bottle of oil weigh in kilograms?
一瓶油，第一次用去1.6千克，第二次用去余下的(3/4)，瓶内还有油2.1千克．这瓶油原来重多少千克．
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1.6 * (3/4)</gadget>
<output>1.2</output>

<gadget id="calculator">2.1 - 1.2</gadget>
<output>0.9</output>

<gadget id="calculator">1.6 + 0.9</gadget>
<output>2.5</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">2.5 / (1/4)</gadget>
<output>10</output>

<result>10</result>