The wall in front of the classroom is 7 meters long and 3 meters wide. There is a blackboard on the wall with an area of 4 square meters. Now it is necessary to paint this wall. If 1 square meter costs 80 yuan, how much will it cost to paint this wall? ?
教室前面的墙壁长7米，宽3米，墙上有一块黑板，面积是4平方米，现在要粉刷这面墙壁，如果1平方米要花80元，那么粉刷这面墙一共要花费多少钱？
<gadget id="calculator">7 * 3</gadget>
<output>21</output>

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

<gadget id="calculator">17 * 80</gadget>
<output>1_360</output>

<result>1_360</result>