The walls of the classroom are 8 meters long and 3 meters wide. There is a window with a side length of 3 meters on the wall. How many square meters will be painted on this wall now?
教室的墙壁，长8米，宽3米．墙上有个边长为3米的窗户．现在要粉刷这面墙壁要粉刷的面积是多少平方米？
<gadget id="calculator">8 * 3</gadget>
<output>24</output>

<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">24 - 9</gadget>
<output>15</output>

<result>15</result>