Polk County supervisors approved a 15-year, $2.5 million loan Tuesday that will help the owners of Merle Hay Mall buy the shuttered Sears and Younkers stores. The stores carry a combined tax valuation of $12.6 million, but the mall owners are said to be offering considerably less than that amount. Meanwhile, Chicago-based Merle Hay Investors also has listed three outlots — locations for Starbucks, IHOP and Applebee’s — for a total of $4.6 million. Ownership also is in the process of renegotiating a development agreement with the city of Des Moines that has been in place since the mall repurposed itself several years ago to offer entertainment options and drive-up storefronts.