The canteen brought a batch of coal and planned to burn 1.8 tons per day, which can last for 20 days. In fact, the canteen burned 2 tons of coal in the first 3 days. According to this calculation, how many days can this batch of coal be burned? (Solve with ratio)
食堂运来一批煤，计划每天烧1.8吨，可以烧20天，实际上食堂前3天一共烧煤2吨．照这样计算，这批煤还可以烧多少天？(用比例解)
<gadget id="calculator">1.8 * 20</gadget>
<output>36</output>

<gadget id="calculator">36 - 2</gadget>
<output>34</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">34 / (2/3)</gadget>
<output>51</output>

<result>51</result>