There is a trapezoidal field with an area of 900 square meters. It is known that the upper bottom is 30 meters long and the lower bottom is 45 meters long. If a canal is dug from the upper bottom to the bottom, what is the shortest length of the canal?
有一块梯形的田地，面积是900平方米．已知它的上底长30米，下底长45米，如果从上底向下底挖一条水渠，这条水渠最短是多少米？
<gadget id="calculator">30 + 45</gadget>
<output>75</output>

<gadget id="calculator">2 / 75</gadget>
<output>2/75 = around 0.026667</output>

<gadget id="calculator">900 * (2/75)</gadget>
<output>24</output>

<result>24</result>