A triangular vegetable field has a base of 90 meters and a height of 40 meters. There are green vegetables and rapeseed in it, and the area of the rapeseed is three times that of the green vegetables. How many square meters is the area for growing vegetables?
一块三角形菜地，底是90米，高是40米，里面种了青菜和油菜，其中油菜的面积是青菜的3倍．种青菜的面积是多少平方米？
<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">1 + 3</gadget>
<output>4</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">90 * 20 * (1/4)</gadget>
<output>450</output>

<result>450</result>