The perimeter of an isosceles triangle is 50 cm. It is known that the ratio of one waist to the base is 3:4. Find the length of the base.
等腰三角形的周长50厘米，已知一条腰与底的比是3：4．求底的长度．
<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">50 * (2/5)</gadget>
<output>20</output>

<result>20</result>