There is a batch of goods in a warehouse, if 3 large trucks are used, it can be shipped in 4 days; if 4 small trucks are used, it can be shipped in 5 days; if 20 trolleys are used, it can be shipped in 6 days. Now use 2 large trucks, 3 small trucks and 7 trolleys to transport together for 2 days, and then switch to trolleys for transportation. The transportation must be completed within two days, so how many trolleys are needed for the next two days?
某仓库内有一批货物，如果用3辆大卡车，4天可以运完；如果用4辆小卡车，5天可以运完；如果用20辆手推车，6天可以运完．现在先用2辆大卡车，3辆小卡车和7辆手推车共同运2天后，全部改用手推车运，必须在两天内运完，那么后两天每天至少需要多少辆手推车？
<gadget id="calculator">1 / 3 / 4</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/12) * 2 * 2</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 / 4 / 5</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/20) * 3 * 2</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 / 20 / 6</gadget>
<output>1/120 = around 0.008333</output>

<gadget id="calculator">(1/120) * 7 * 2</gadget>
<output>7/60 = around 0.116667</output>

<gadget id="calculator">(1/3) + (3/10) + (7/60)</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">(1/4) / (1/120) / 2</gadget>
<output>15</output>

<result>15</result>