A workshop plans to produce 800 parts, and 80 were produced in the first 4 days. According to this calculation, how many days are left for production? (Solve it in two ways, one of which is a proportional solution)
某车间计划生产800个零件，前4天生产了80个，照这样计算，剩下的还要生产多少天？(用两种方法解，其中一种用比例解)
<gadget id="calculator">800 - 80</gadget>
<output>720</output>

<gadget id="calculator">80 / 4</gadget>
<output>20</output>

<gadget id="calculator">720 / 20</gadget>
<output>36</output>

<result>36</result>