I want to find if one item sold this month is also sold in last month. If
so, return the quantify sold last month. How do I do that? thanks a lot.

that is-- to match column 1 and column 3 and then return the value of column 4

column 1 item name sold in this month
column 2 item quantity sold this month

column 3 item name sold last month
column 4 item quantify sold last month