Uncle Wang brought 800 yuan to buy chemical fertilizer, 42 yuan per bag of fertilizer, and 170 yuan left after buying fertilizer. How many bags of fertilizer did Uncle Wang buy?
王大伯带800元买化肥，每袋化肥42元，买化肥后剩下170元，王大伯买化肥多少袋？
<gadget id="calculator">800 - 170</gadget>
<output>630</output>

<gadget id="calculator">630 / 42</gadget>
<output>15</output>

<result>15</result>