To process a batch of parts, 120 were processed in the first 3 hours, and then 180 were processed at the same speed. How many hours did it take? (Please use multiple methods to answer)
加工一批零件，前3小时加工了120个，后来又以同样的速度加工了180个，一共用了几小时？(请用多种方法解答)
<gadget id="calculator">120 / 3</gadget>
<output>40</output>

<gadget id="calculator">180 / 40</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">(9/2) + 3</gadget>
<output>15/2 = around 7.5</output>

<result>15/2 = around 7.5</result>