The incubation period of a chicken is 21 days, which is 3/4 of that of a duck. How many days is the incubation period of a duck?
鸡的孵化期是21天，是鸭的孵化期的(3/4)，鸭的孵化期是多少天．
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">21 / (3/4)</gadget>
<output>28</output>

<result>28</result>