The cross section of a canal is trapezoidal. It is known that the upper base of the ladder is 3.2 meters, the height is 1.5 meters, and the area of the cross section is 33 square meters. Find the lower base. (solution by equation)
一条水渠的横截面是梯形，已知梯行的上底是3.2米，高是1.5米，横截面的面积是33平方米，求下底．(用方程解)
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) * 1.5 * 3.2</gadget>
<output>2.4</output>

<gadget id="calculator">33 - 2.4</gadget>
<output>30.6</output>

<gadget id="calculator">(1/2) * 1.5</gadget>
<output>0.75</output>

<gadget id="calculator">30.6 / 0.75</gadget>
<output>40.8</output>

<result>40.8</result>