A total of 750 kilograms of rice and flour are shipped from the school cafeteria. When 1/3 of the rice and 3/5 of the flour are used, there are 420 kilograms left. How many kilograms of flour are shipped?
学校食堂运来大米和面粉共750千克，当用去大米的(1/3)和面粉的(3/5)时，还剩下420千克，运来面粉多少千克？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">750 * (1/3)</gadget>
<output>250</output>

<gadget id="calculator">750 - 250 - 420</gadget>
<output>80</output>

<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">(3/5) - (1/3)</gadget>
<output>4/15 = around 0.266667</output>

<gadget id="calculator">80 / (4/15)</gadget>
<output>300</output>

<result>300</result>