A newly dug drainage channel, excavated 9 cubic meters. The cross section of the canal is trapezoidal, with a width of 0.5 meters at the upper base, a width of 0.4 meters at the lower base, and a depth of 0.4 meters. How long is this drain? (solution by equation)
新挖的一条排水渠，挖土9立方米．水渠的横截面是梯形，上底宽0.5米，下底宽0.4米，深0.4米．这条排水渠长多少米？(用方程解)
<gadget id="calculator">0.4 / 2</gadget>
<output>0.2</output>

<gadget id="calculator">0.5 * 0.2</gadget>
<output>0.1</output>

<gadget id="calculator">0.4 * 0.2</gadget>
<output>0.08</output>

<gadget id="calculator">0.1 + 0.08</gadget>
<output>0.18</output>

<gadget id="calculator">9 / 0.18</gadget>
<output>50</output>

<result>50</result>