There is a wall to be painted at home. It is known that the length of this wall is 7m and the width is 3m. There is a TV wall with an area of 4m**2 on the wall that is not painted. What is the area to be painted in m**2?
家里要刷一面墙，已知这面墙长是7m，宽是3m，墙上有一面面积是4m**2的电视墙不刷，要粉刷的面积是多少m**2？
<gadget id="calculator">7 * 3</gadget>
<output>21</output>

<gadget id="calculator">21 - 4</gadget>
<output>17</output>

<result>17</result>