A small barrage has a cross-sectional upper base of 35 meters, a lower base of 64 meters, and a height of 15 meters. What is the cross-sectional area of this barrage in square meters?
一座小型拦河坝，横截面的上底是35米，下底是64米，高是15米，这座拦河坝的横截面积是多少平方米？
<gadget id="calculator">35 + 64</gadget>
<output>99</output>

<gadget id="calculator">15 / 2</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">99 * (15/2)</gadget>
<output>1_485/2 = around 742.5</output>

<result>1_485/2 = around 742.5</result>