A trapezoid has an upper base of 2 cm, a lower base of 2.8 cm, and a height of 9 cm. Two such trapezoids can be put together to form a parallelogram with a height of 9 cm and a base of cm.
一个梯形的上底是2厘米，下底是2.8厘米，高是9厘米．用两个这样的梯形可以拼成一个高9厘米，底是多少厘米的平行四边形．
<gadget id="calculator">2 + 2.8</gadget>
<output>4.8</output>

<result>4.8</result>