During the busy farming season, a wheat field needs to be mowed. Farm A is contracted alone, and it takes 20 days to complete the cutting. Farm B is contracted alone, and it cuts 2 acres less than A every day. Now, in order to save time, A and B cooperate in the contract. It will take 6 days for B to finish the rest alone. How many acres of grass are there in this wheat field?
农忙季节，一块麦田需要割草．甲农场单独承包，需要20天割完，乙农场单独承包，每天比甲少割2亩，现为了节省时间，由甲乙合作承包，当完成了(3/4)时，甲因有事临时退出，剩下的由乙单独完成还需6天．请问这块麦田共有多少亩草．
<gadget id="calculator">2 * 6</gadget>
<output>12</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/20) * 6</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

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

<gadget id="calculator">(3/10) + (-1/4)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">12 / (1/20)</gadget>
<output>240</output>

<result>240</result>