The grain store shipped 30 bags of flour and 45 bags of rice, weighing a total of 3,900 kilograms. Each bag of flour weighs 70 kilograms. How many kilograms does each bag of rice weigh?
粮店运来30袋面粉和45袋大米，共重3900千克，每袋面粉重70千克，每袋大米重多少千克？
<gadget id="calculator">70 * 30</gadget>
<output>2_100</output>

<gadget id="calculator">3_900 - 2_100</gadget>
<output>1_800</output>

<gadget id="calculator">1_800 / 45</gadget>
<output>40</output>

<result>40</result>