The upper base of an isosceles trapezoid is 8 cm, the lower base is 6 cm, and the length of a waist is 7 cm. How many centimeters of iron wire is required to enclose this isosceles trapezoid?
一个等腰梯形的上底是8厘米，下底是6厘米，一条腰长7厘米，围成这个等腰梯形至少要多少厘米长的铁丝．
<gadget id="calculator">8 + 6 + 7 + 7</gadget>
<output>28</output>

<result>28</result>