The small shop next to the school sells a batch of small balls, the purchase price is 1.5 yuan each, and the selling price is 2 yuan each. When there are only 20 balls left, they start selling at a 10% discount. After all the balls are sold out, the total profit is 86 yuan. So how many balls are there in total?
学校旁边的小店卖一批小皮球，进价每只1.5元，卖出价每只2元．当卖到只剩下20只皮球时，开始让利销售，以九折出售，皮球全部卖完后，共得利润86元．那么这批皮球一共有多少只．
<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">20 * 1.5</gadget>
<output>30</output>

<gadget id="calculator">20 * 2 * 0.9</gadget>
<output>36</output>

<gadget id="calculator">86 - 30 - 36</gadget>
<output>20</output>

<gadget id="calculator">40 + 30 + 20</gadget>
<output>90</output>

<gadget id="calculator">2 - 1.5</gadget>
<output>0.5</output>

<gadget id="calculator">90 / 0.5</gadget>
<output>180</output>

<result>180</result>