There is a dam whose cross section is trapezoidal, its area is 76.5 square meters, its height is 9 meters, and its width is 5 meters. How wide is the bottom of the dam? (use equation and column method to solve problems)
有一个水坝横截面是梯形，它的面积是76.5平方米，高是9米，坝面宽是5米．坝底有多宽？(使用方程和列式方法解题)
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) * 9 * 5</gadget>
<output>45/2 = around 22.5</output>

<gadget id="calculator">76.5 - (45/2)</gadget>
<output>54</output>

<gadget id="calculator">(1/2) * 9</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">54 / (9/2)</gadget>
<output>12</output>

<result>12</result>