The school has to repaint the walls of the classrooms (except floors and ceilings). It is known that the length of each classroom is 9 meters, the width is 6 meters, and the height is 3.5 meters. The area after deducting doors, windows and blackboards is 20 square meters. If it costs 5 yuan per square meter, how much does it cost to paint such a classroom?
学校要重新粉刷教室的四壁(地板与天花板除外)．已知每个教室的长是9米，宽是6米，高是3.5米，扣除门窗、黑板的面积20平方米．如果每平方米需花费5元钱，粉刷这样一个教室需要多少钱？
<gadget id="calculator">9 * 3.5</gadget>
<output>31.5</output>

<gadget id="calculator">6 * 3.5</gadget>
<output>21</output>

<gadget id="calculator">31.5 + 21</gadget>
<output>52.5</output>

<gadget id="calculator">52.5 * 2</gadget>
<output>105</output>

<gadget id="calculator">105 - 20</gadget>
<output>85</output>

<gadget id="calculator">85 * 5</gadget>
<output>425</output>

<result>425</result>