A classroom wall is 4 meters long and 3 meters wide. There is a blackboard on the wall with an area of 3 square meters. Now this wall is going to be painted, how big is the area to be painted?
教室的一面墙长4米，宽3米．墙上有一块黑板，面积是3平方米．现在要粉刷这面墙壁，要粉刷的面积有多大？
<gadget id="calculator">4 * 3</gadget>
<output>12</output>

<gadget id="calculator">12 - 3</gadget>
<output>9</output>

<result>9</result>