A kind of concrete is prepared according to the ratio of cement, sand and gravel at 3:5:6. How many kilograms of stones should be prepared to prepare 2800 kilograms of this concrete?
一种混凝土是按水泥、砂、石子的比为3：5：6配制而成．要配制这种混凝土2800千克，应准备石子多少千克？
<gadget id="calculator">3 + 5 + 6</gadget>
<output>14</output>

<gadget id="calculator">6 / 14</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">2_800 * (3/7)</gadget>
<output>1_200</output>

<result>1_200</result>