parallelogram formed by two identical trapezoids has an area of 60 square centimeters and a height of 4 centimeters. What is the sum of the top and bottom of each trapezoid in centimeters?
两个完全一样的梯形拼成的平行四边形面积是60平方厘米，高是4厘米．每个梯形上、下的和是多少厘米．
<gadget id="calculator">60 / 2</gadget>
<output>30</output>

<gadget id="calculator">2 / 4</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">30 * (1/2)</gadget>
<output>15</output>

<result>15</result>