The area of a trapezoid is 18 square centimeters, its height is 5 centimeters, and its upper base is 2.8 centimeters. How many centimeters is the bottom.
一个梯形的面积是18平方厘米，它的高是5厘米，上底为2.8厘米．下底是多少厘米．
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">18 * (2/5)</gadget>
<output>36/5 = around 7.2</output>

<gadget id="calculator">(36/5) - 2.8</gadget>
<output>4.4</output>

<result>4.4</result>