The lengths of the three sides of an isosceles trapezoid are 55 cm, 25 cm, and 15 cm respectively, and its lower base is the longest side. So, what is the length of one side of this isosceles trapezoid?
一个等腰梯形中三条边的长分别是55厘米、25厘米、15厘米，并且它的下底是最长的一条边．那么，这个等腰梯形的一个腰长是多少厘米．
<result>25</result>