Divide a rectangle with an area of 60 square centimeters into 4 different triangles. The area of the green triangle accounts for 15% of the area of the rectangle, the area of the yellow part is 28 square centimeters, and the area of the red part is 12 square centimeters. Find the value of the blue triangle area.
把一个面积是60平方厘米的长方形分成4个不同的三角形，绿色三角形的面积占长方形面积的15%，黄色部分的面积为28平方厘米，红色部分的面积为12平方厘米，求蓝色三角形的面积．
<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">60 * (3/20)</gadget>
<output>9</output>

<gadget id="calculator">60 - 9 - 12 - 28</gadget>
<output>11</output>

<result>11</result>