A 50 cm long iron wire is used to form an isosceles trapezoid whose upper base is 8 cm long and the lower base is 12 cm long. What is the length of one side of this trapezoid?
把一根长50厘米的铁丝，围成一个上底长8厘米，下底长12厘米的等腰梯形．这个梯形的一条腰长多少厘米．
<gadget id="calculator">50 - 8 - 12</gadget>
<output>30</output>

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<result>15</result>