A produces 15 parts per hour and B produces 12 parts per hour. Once, A and B produced the same number of parts at the same time, and as a result, A completed the task 4 hours earlier than B. How many parts did A produce in total?
甲每小时生产15个零件，乙每小时生产12个零件．一次，甲乙同时生产同样多的零件，结果甲比乙提前4小时完成任务．甲一共生产了多少个零件．
<gadget id="calculator">15 - 12</gadget>
<output>3</output>

<gadget id="calculator">4 / 3</gadget>
<output>4/3 = around 1.333333</output>

<gadget id="calculator">15 * (4/3) * 15</gadget>
<output>300</output>

<result>300</result>