The supermarket bought a batch of fruit, originally planned to sell 20 boxes per day, and sold out in 15 days, but actually only sold 75% of the original plan every day, how many days did it actually sell out?
超市进了一批水果，原计划每天卖20箱，15天卖完，实际每天只卖了原计划的75%，实际几天卖完？
<gadget id="calculator">20 * 15</gadget>
<output>300</output>

<gadget id="calculator">75 / 100</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">20 * (3/4)</gadget>
<output>15</output>

<gadget id="calculator">300 / 15</gadget>
<output>20</output>

<result>20</result>