For a barrel of oil, 1/3 of the total is poured out for the first time, 16 liters are poured out for the second time, and there are 20 liters left, how many liters of oil are poured out for the first time?
一桶油，第一次倒出了总数的(1/3)，第二次倒出16升，还有20升，第一次倒出油多少升？
<gadget id="calculator">16 + 20</gadget>
<output>36</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">36 / (2/3)</gadget>
<output>54</output>

<gadget id="calculator">54 * (1/3)</gadget>
<output>18</output>

<result>18</result>