Use 84 cm wire to form a triangle. The ratio of the lengths of the three sides of this triangle is 3:4:5. What is the length of the shortest side of this triangle in centimeters?
用84厘米的铁丝围成一个三角形，这个三角形三条边长度的比是3：4：5，这个三角形最短的边长是多少厘米？
<gadget id="calculator">3 + 4 + 5</gadget>
<output>12</output>

<gadget id="calculator">3 / 12</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">84 * (1/4)</gadget>
<output>21</output>

<result>21</result>