Yesterday, 180 tons of garbage were transported to the garbage cleaning site, and it took 4 hours to clean them up; today, 9 tons more garbage was transported than yesterday. How many hours will it take to clean up today?
垃圾清理场昨天运来垃圾180吨，用了4小时清理完毕；今天运来的垃圾比昨天多了9吨，今天需要几小时才能清理完毕？
<gadget id="calculator">180 + 9</gadget>
<output>189</output>

<gadget id="calculator">180 / 4</gadget>
<output>45</output>

<gadget id="calculator">189 / 45</gadget>
<output>21/5 = around 4.2</output>

<result>21/5 = around 4.2</result>