If the lengths of two adjacent sides of a parallelogram are 7 cm and 8 cm, what is its perimeter in cm?
一个平行四边形相邻的两条边的长度是7厘米和8厘米，它的周长是多少厘米．
<gadget id="calculator">7 + 7 + 8 + 8</gadget>
<output>30</output>

<result>30</result>