Someone goes to a fast food restaurant to work as a summer job. The monthly salary (30 days) is 800 yuan and a set of hat, shoes and overalls. Due to other reasons, she only worked for 20 days and received 500 yuan (the labor insurance supplies do not need to be returned), please calculate how much the labor insurance supplies should be worth.
某人到快餐店打暑期工，一个月(30天计)报酬为800元和发给帽，鞋和工作服一套．她由于另有原因，只工作了20天，得到500元，(劳保用品不用交回)，请算算劳保用品应值多少元．
<gadget id="calculator">800 - 500</gadget>
<output>300</output>

<gadget id="calculator">300 * 2</gadget>
<output>600</output>

<gadget id="calculator">600 - 500</gadget>
<output>100</output>

<result>100</result>