A batch of parts can be processed by A and B in 24 hours. Now A alone can do it for 16 hours, and then B can do it again for 3 hours. A total of (9/20) of this batch of parts has been completed. It is also known that A is faster than B per hour. Process 4 more. How many parts are there in this batch?
加工一批零件，甲乙合做24小时可以完成，现由甲独做16小时，然后乙再度作3小时，共完成了这批零件的(9/20)，又知甲每小时比乙每小时多加工4个．这批零件有多少个？
<gadget id="calculator">9 / 20</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">1 / 24</gadget>
<output>1/24 = around 0.041667</output>

<gadget id="calculator">(1/24) * 3</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">(9/20) - (1/8)</gadget>
<output>13/40 = around 0.325</output>

<gadget id="calculator">16 - 3</gadget>
<output>13</output>

<gadget id="calculator">(13/40) / 13</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">(1/24) - (1/40)</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">(1/40) - (1/60)</gadget>
<output>1/120 = around 0.008333</output>

<gadget id="calculator">4 / (1/120)</gadget>
<output>480</output>

<result>480</result>