Build a barrage with a trapezoidal cross section. The upper base of the barrage cross section is 2 meters, the lower base is 10 decimeters, the height is 3 meters, and the length of the barrage is 100 meters. How much earth and stone is needed in total.
修一条横截面为梯形的拦河坝，拦河坝横截面的上底是2米，下底是10分米，高是3米，拦河坝的长是100米．一共需要多少方土石．
<gadget id="calculator">10 / 10</gadget>
<output>1</output>

<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<gadget id="calculator">3 / 2</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">3 * (3/2) * 100</gadget>
<output>450</output>

<result>450</result>