There is a batch of apples in the fruit shop. After selling (1/3), another 420 kg is shipped in. At this time, the mass of the apples is more than the original (1/4). How many kilograms of apples are there in the fruit shop?
水果店有一批苹果，卖掉(1/3)后，又运进420千克，这时苹果的质量比原来多(1/4)．水果店原有苹果多少千克？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 + (1/4)</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">(5/4) - (2/3)</gadget>
<output>7/12 = around 0.583333</output>

<gadget id="calculator">420 / (7/12)</gadget>
<output>720</output>

<result>720</result>