Two identical trapezoids are put together to form a parallelogram with a base of 15 cm and a height of 8 cm. It is known that the upper base of the trapezoid is 5 cm and the lower base is how many cm.
两个完全一样的梯形拼成一个底为15厘米，高为8厘米的平行四边形，已知梯形的上底为5厘米，下底是多少厘米．
<gadget id="calculator">15 - 5</gadget>
<output>10</output>

<result>10</result>