Zhang Hua has a bag of yellow, blue, green and red balls, of which 25% are green, 10% are yellow, and the remaining 20% are blue. If there are 15 blue balls, How many red balls are there in this bag?
张华有一袋黄、蓝、绿、红四种颜色的球，其中25%是绿色的，10%是黄色的，余下的球中20%是蓝色的，如果蓝色的球是15个，那么这包球中红色的球有多少个．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">15 / (1/5)</gadget>
<output>75</output>

<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 - (3/20) - (1/10)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">75 / (3/4)</gadget>
<output>100</output>

<gadget id="calculator">100 * (3/4)</gadget>
<output>75</output>

<gadget id="calculator">75 - 15</gadget>
<output>60</output>

<result>60</result>