There are several red and white balls in the kindergarten. Originally, the number of white balls accounted for 60% of the total. Later, 30 red balls were bought, and the number of white balls accounted for 40% of the total. How many white balls are there?
幼儿园有红色和白色两种颜色的皮球若干个，原来白皮球的个数占总数的60%，后来又买进了30个红皮球，这时白皮球的个数占总数的40%．白皮球有多少个？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">(3/5) / (2/5)</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">60 / 100</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) / (3/5)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">(3/2) - (2/3)</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">30 / (5/6)</gadget>
<output>36</output>

<result>36</result>