A, B, and C process a total of 1000 parts. The ratio of A and B's completed quantity is 7:5, C completed 64 parts less than A, how many parts has B completed.
甲、乙、丙三人共加工1000个零件．甲、乙两人完成数量的比是7：5，丙比甲少完成64个零件，乙完成了多少个零件．
<gadget id="calculator">1_000 + 64</gadget>
<output>1_064</output>

<gadget id="calculator">7 + 5 + 7</gadget>
<output>19</output>

<gadget id="calculator">5 / 19</gadget>
<output>5/19 = around 0.263158</output>

<gadget id="calculator">1_064 * (5/19)</gadget>
<output>280</output>

<result>280</result>