A batch of parts is completed in 12 days by A alone, 15 days by B alone, and 2 days by two people. A makes 30 more parts than B. How many parts are there in total?
一批零件甲独做12天完成，乙独做15天完成，两人合做2天，甲比乙多做30个，这批零件共有多少个？
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">2 / 15</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">(1/6) - (2/15)</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">30 / (1/30)</gadget>
<output>900</output>

<result>900</result>