Master Zhang processes a batch of parts. The ratio of the number of completed parts to the number of unfinished parts on the first day is 2:3. If 12 more parts are processed, half of this batch of parts can be completed. How many parts are there in total?
张师傅加工一批零件，第一天完成的个数与未完成零件的个数比是2：3，如果再加工12个零件，就可完成这批零件的一半，这批零件共多少个？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">2 + 3</gadget>
<output>5</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(1/2) - (2/5)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">12 / (1/10)</gadget>
<output>120</output>

<result>120</result>