A batch of chemical fertilizer is used up (3/4), leaving 20 tons. How many tons is this batch of fertilizer? What is the correct column
一批化肥，用去(3/4)，还剩20吨．这批化肥有多少吨？列式正确的是多少
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

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

<gadget id="calculator">20 / (1/4)</gadget>
<output>80</output>

<result>80</result>