total of 21 small trees are planted on one side of a canal. The distance between every two small trees is (3/2) meters. What is the minimum length of this canal?
在一条水渠的一边共种了21棵小树，每两棵小树之间的距离是(3/2)米，这条水渠至少长多少米．
<gadget id="calculator">3 / 2</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">21 - 1</gadget>
<output>20</output>

<gadget id="calculator">(3/2) * 20</gadget>
<output>30</output>

<result>30</result>