The wall in front of the classroom is 6 meters long and 3 meters wide. There is a blackboard on the wall, which is 3 meters long and 1 meter wide. Now this wall is to be painted. How many square meters is the wall to be painted?
教室前面的墙壁，长6米，宽3米，墙上有一块黑板，长3米，宽1米，现在要粉刷这面墙壁，要粉刷的墙壁是多少平方米？
<gadget id="calculator">6 * 3</gadget>
<output>18</output>

<gadget id="calculator">3 * 1</gadget>
<output>3</output>

<gadget id="calculator">18 - 3</gadget>
<output>15</output>

<result>15</result>