A newly dug canal has a trapezoidal cross-section. The mouth of the canal is 2.8m wide, the bottom of the canal is 1.2m wide, and the canal is 2.5m deep. What is its cross-sectional area?
一条新挖的水渠，横截面是梯形．渠口宽2.8m，渠底宽1.2m，渠深2.5m．它的横截面的面积是多少？
<gadget id="calculator">1.2 + 2.8</gadget>
<output>4</output>

<gadget id="calculator">2.5 / 2</gadget>
<output>1.25</output>

<gadget id="calculator">4 * 1.25</gadget>
<output>5</output>

<result>5</result>