The perimeter of an isosceles triangle is 70 cm, and the ratio of the length of one waist to the base is 3:4. How many centimeters is the base of this triangle?
等腰三角形的周长是70厘米，一条腰与底边长度的比是3：4，这个三角形的底边是多少厘米？
<gadget id="calculator">3 + 3 + 4</gadget>
<output>10</output>

<gadget id="calculator">4 / 10</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">70 * (2/5)</gadget>
<output>28</output>

<result>28</result>