The bookshelf is divided into upper and lower layers, and there are 130 books of various types. It is known that 80 books are stored in the lower layer, and how many books are stored in the upper layer? (column equation solution)
书架分上、下两层，共存各类书130本，已知下层存放80本，上层存放多少本？(列方程解答)
<gadget id="calculator">130 - 80</gadget>
<output>50</output>

<result>50</result>