To build a canal with a length of 1800 meters, after 5 days of work, the repaired accounts for the unrepaired (1/3). According to this progress, how many days will it take to complete the canal?
修一条长1800米的水渠，工作5天后，已修的占未修的(1/3)．照这样的进度，还要多少天才能修完这条水渠？
<gadget id="calculator">1 + 3</gadget>
<output>4</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

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

<gadget id="calculator">1_800 * (1/20)</gadget>
<output>90</output>

<gadget id="calculator">1_800 / 90</gadget>
<output>20</output>

<gadget id="calculator">20 - 5</gadget>
<output>15</output>

<result>15</result>