There are 789 chickens in the farm, and the number of chickens is 69 less than twice that of ducks. How many ducks are there in the farm?
养殖场有789只鸡，鸡的只数比鸭的2倍少69只．养殖场有多少只鸭？
<gadget id="calculator">789 + 69</gadget>
<output>858</output>

<gadget id="calculator">858 / 2</gadget>
<output>429</output>

<result>429</result>