The ratio of the number of melons to the number of watermelons in the fruit shop is 3:8. If 15 melons and 36 watermelons are sold every day, after a few days, the melons are sold out and there are 20 watermelons left. How many watermelons are there in the fruit shop?
水果店里香瓜个数和西瓜个数的比是3：8，如果每天卖香瓜15个，西瓜36个，若干天后，香瓜正好卖完，西瓜还剩20个，水果店原有西瓜多少个？
<gadget id="calculator">3 / 8</gadget>
<output>3/8 = around 0.375</output>

<gadget id="calculator">(3/8) * 20</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">(3/8) * 36</gadget>
<output>27/2 = around 13.5</output>

<gadget id="calculator">15 - (27/2)</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">(15/2) / (3/2)</gadget>
<output>5</output>

<gadget id="calculator">36 * 5</gadget>
<output>180</output>

<gadget id="calculator">180 + 20</gadget>
<output>200</output>

<result>200</result>